<?xml version="1.0" encoding="us-ascii"?>
<!--XBRL document created with Toppan Merrill Bridge  9.6.7556.35618 -->
<!--Based on XBRL 2.1-->
<!--Created on: 11/5/2020 1:06:16 PM-->
<!--Modified on: 11/5/2020 1:06:16 PM-->
<schema xmlns:us-types="http://fasb.org/us-types/2019-01-31" xmlns:invest="http://xbrl.sec.gov/invest/2013-01-31" xmlns:num="http://www.xbrl.org/dtr/type/numeric" xmlns:currency="http://xbrl.sec.gov/currency/2019-01-31" xmlns:dei="http://xbrl.sec.gov/dei/2019-01-31" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:country="http://xbrl.sec.gov/country/2017-01-31" xmlns:naics="http://xbrl.sec.gov/naics/2017-01-31" xmlns:us-gaap="http://fasb.org/us-gaap/2019-01-31" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:stpr="http://xbrl.sec.gov/stpr/2018-01-31" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:sic="http://xbrl.sec.gov/sic/2011-01-31" xmlns:exch="http://xbrl.sec.gov/exch/2019-01-31" xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ardelyx.com/20200930" attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:ardx="http://www.ardelyx.com/20200930">
  <annotation>
    <appinfo>
      <link:roleType roleURI="http://www.ardelyx.com/role/StatementCondensedBalanceSheets" id="StatementCondensedBalanceSheets">
        <link:definition>00100 - Statement - CONDENSED BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/StatementCondensedStatementsOfOperationsAndComprehensiveLoss" id="StatementCondensedStatementsOfOperationsAndComprehensiveLoss">
        <link:definition>00200 - Statement - CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/StatementCondensedStatementsOfCashFlows" id="StatementCondensedStatementsOfCashFlows">
        <link:definition>00400 - Statement - CONDENSED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCashCashEquivalentsAndShortTermInvestmentsScheduleOfSecuritiesClassifiedAsCashCashEquivalentsAndShortTermInvestmentsDetails" id="DisclosureCashCashEquivalentsAndShortTermInvestmentsScheduleOfSecuritiesClassifiedAsCashCashEquivalentsAndShortTermInvestmentsDetails">
        <link:definition>40201 - Disclosure - Cash, Cash Equivalents and Short-Term Investments - Schedule of Securities Classified as Cash, Cash Equivalents and Short-Term Investments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureBorrowingsDetailsCalc2" id="DisclosureBorrowingsDetailsCalc2">
        <link:definition>40601 - Disclosure - Borrowings (Details) - Calc2</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureLeasesBalanceSheetAndStatementOfOperationsDetails" id="DisclosureLeasesBalanceSheetAndStatementOfOperationsDetails">
        <link:definition>40601 - Disclosure - Leases - Balance Sheet and Statement of Operations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureLeasesUndiscountedCashPaymentObligationsDetails" id="DisclosureLeasesUndiscountedCashPaymentObligationsDetails">
        <link:definition>40602 - Disclosure - Leases - Undiscounted Cash Payment Obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureLeasesUndiscountedCashPaymentObligationsDetailsCalc2" id="DisclosureLeasesUndiscountedCashPaymentObligationsDetailsCalc2">
        <link:definition>40602 - Disclosure - Leases - Undiscounted Cash Payment Obligations (Details) Calc 2</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DocumentDocumentAndEntityInformation" id="DocumentDocumentAndEntityInformation">
        <link:definition>00090 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/StatementCondensedStatementsOfChangesInStockholdersEquity" id="StatementCondensedStatementsOfChangesInStockholdersEquity">
        <link:definition>00300 - Statement - CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureDerivativeLiability" id="DisclosureDerivativeLiability">
        <link:definition>10401 - Disclosure - Derivative Liability</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureOrganizationAndBasisOfPresentationPriorPeriodErrorsDetails" id="DisclosureOrganizationAndBasisOfPresentationPriorPeriodErrorsDetails">
        <link:definition>40102 - Disclosure - Organization and Basis of Presentation - Prior Period Errors (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureOrganizationAndBasisOfPresentationLiquidityDetails" id="DisclosureOrganizationAndBasisOfPresentationLiquidityDetails">
        <link:definition>40104 - Disclosure - Organization and Basis of Presentation - Liquidity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCashCashEquivalentsAndShortTermInvestmentsAdditionalInformationDetails" id="DisclosureCashCashEquivalentsAndShortTermInvestmentsAdditionalInformationDetails">
        <link:definition>40202 - Disclosure - Cash, Cash Equivalents and Short-Term Investments - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureFairValueMeasurementsSummaryOfFairValueMeasurementsOfCompanySFinancialAssetsAndLiabilitiesDetails" id="DisclosureFairValueMeasurementsSummaryOfFairValueMeasurementsOfCompanySFinancialAssetsAndLiabilitiesDetails">
        <link:definition>40301 - Disclosure - Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets and Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureDerivativeLiabilityAdditionalInformationDetails" id="DisclosureDerivativeLiabilityAdditionalInformationDetails">
        <link:definition>40401 - Disclosure - Derivative Liability - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureBorrowingDetails" id="DisclosureBorrowingDetails">
        <link:definition>40501 - Disclosure - Borrowing (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureEquityIncentivePlansAdditionalInformationDetails" id="DisclosureEquityIncentivePlansAdditionalInformationDetails">
        <link:definition>40701 - Disclosure - Equity Incentive Plans - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureEquityIncentivePlansSummaryOfStockBasedCompensationExpenseRecognizedDetails" id="DisclosureEquityIncentivePlansSummaryOfStockBasedCompensationExpenseRecognizedDetails">
        <link:definition>40702 - Disclosure - Equity Incentive Plans - Summary of Stock-Based Compensation Expense Recognized (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureEquityIncentivePlansUnrecognizedStockBasedCompensationDetails" id="DisclosureEquityIncentivePlansUnrecognizedStockBasedCompensationDetails">
        <link:definition>40703 - Disclosure - Equity Incentive Plans - Unrecognized Stock-Based Compensation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureStockholdersEquityDetails" id="DisclosureStockholdersEquityDetails">
        <link:definition>40801 - Disclosure - Stockholders' Equity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureNetLossPerShareAdditionalInformationDetails" id="DisclosureNetLossPerShareAdditionalInformationDetails">
        <link:definition>40902 - Disclosure - Net Loss Per Share - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCollaborationAndLicensingAgreementsAdditionalInformationDetails" id="DisclosureCollaborationAndLicensingAgreementsAdditionalInformationDetails">
        <link:definition>41001 - Disclosure - Collaboration and Licensing Agreements - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCollaborationAndLicensingAgreementsScheduleOfChangesInDeferredRevenueDetails" id="DisclosureCollaborationAndLicensingAgreementsScheduleOfChangesInDeferredRevenueDetails">
        <link:definition>41002 - Disclosure - Collaboration and Licensing Agreements - Schedule of Changes in Deferred Revenue (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureSubsequentEventsAdditionalInformationDetails" id="DisclosureSubsequentEventsAdditionalInformationDetails">
        <link:definition>41301 - Disclosure - Subsequent Events - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/StatementCondensedBalanceSheetsParenthetical" id="StatementCondensedBalanceSheetsParenthetical">
        <link:definition>00105 - Statement - CONDENSED BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureOrganizationAndBasisOfPresentation" id="DisclosureOrganizationAndBasisOfPresentation">
        <link:definition>10101 - Disclosure - Organization and Basis of Presentation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCashCashEquivalentsAndShortTermInvestments" id="DisclosureCashCashEquivalentsAndShortTermInvestments">
        <link:definition>10201 - Disclosure - Cash, Cash Equivalents and Short-Term Investments</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureFairValueMeasurements" id="DisclosureFairValueMeasurements">
        <link:definition>10301 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureBorrowing" id="DisclosureBorrowing">
        <link:definition>10501 - Disclosure - Borrowing</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureLeases" id="DisclosureLeases">
        <link:definition>10601 - Disclosure - Leases</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureEquityIncentivePlans" id="DisclosureEquityIncentivePlans">
        <link:definition>10701 - Disclosure - Equity Incentive Plans</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureStockholdersEquity" id="DisclosureStockholdersEquity">
        <link:definition>10801 - Disclosure - Stockholders' Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureNetLossPerShare" id="DisclosureNetLossPerShare">
        <link:definition>10901 - Disclosure - Net Loss Per Share</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCollaborationAndLicensingAgreements" id="DisclosureCollaborationAndLicensingAgreements">
        <link:definition>11001 - Disclosure - Collaboration and Licensing Agreements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureContingencies" id="DisclosureContingencies">
        <link:definition>11101 - Disclosure - Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureIncomeTaxes" id="DisclosureIncomeTaxes">
        <link:definition>11201 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureSubsequentEvents" id="DisclosureSubsequentEvents">
        <link:definition>11301 - Disclosure - Subsequent Events</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureOrganizationAndBasisOfPresentationPolicies" id="DisclosureOrganizationAndBasisOfPresentationPolicies">
        <link:definition>20102 - Disclosure - Organization and Basis of Presentation (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCashCashEquivalentsAndShortTermInvestmentsTables" id="DisclosureCashCashEquivalentsAndShortTermInvestmentsTables">
        <link:definition>30203 - Disclosure - Cash, Cash Equivalents and Short-Term Investments (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureFairValueMeasurementsTables" id="DisclosureFairValueMeasurementsTables">
        <link:definition>30303 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureDerivativeLiabilityTables" id="DisclosureDerivativeLiabilityTables">
        <link:definition>30403 - Disclosure - Derivative Liability (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureBorrowingTables" id="DisclosureBorrowingTables">
        <link:definition>30503 - Disclosure - Borrowing (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureLeasesTables" id="DisclosureLeasesTables">
        <link:definition>30603 - Disclosure - Leases (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureEquityIncentivePlansTables" id="DisclosureEquityIncentivePlansTables">
        <link:definition>30703 - Disclosure - Equity Incentive Plans (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureNetLossPerShareTables" id="DisclosureNetLossPerShareTables">
        <link:definition>30903 - Disclosure - Net Loss Per Share (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureCollaborationAndLicensingAgreementsTables" id="DisclosureCollaborationAndLicensingAgreementsTables">
        <link:definition>31003 - Disclosure - Collaboration and Licensing Agreements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureOrganizationAndBasisOfPresentationAdditionalInformationDetails" id="DisclosureOrganizationAndBasisOfPresentationAdditionalInformationDetails">
        <link:definition>40101 - Disclosure - Organization and Basis of Presentation - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureDerivativeLiabilityScheduleOfChangesInFairValueDetails" id="DisclosureDerivativeLiabilityScheduleOfChangesInFairValueDetails">
        <link:definition>40402 - Disclosure - Derivative Liability - Schedule of Changes in Fair Value (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureNetLossPerShareComputationOfBasicAndDilutedLossPerShareAttributableToCommonStockholdersDetails" id="DisclosureNetLossPerShareComputationOfBasicAndDilutedLossPerShareAttributableToCommonStockholdersDetails">
        <link:definition>40901 - Disclosure - Net Loss Per Share - Computation of Basic and Diluted Loss Per Share Attributable to Common Stockholders (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/role/DisclosureContingenciesAdditionalInformationDetails" id="DisclosureContingenciesAdditionalInformationDetails">
        <link:definition>41101 - Disclosure - Contingencies - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:type="simple" xlink:href="ardx-20200930_pre.xml" xlink:title="Presentation Links, all" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="ardx-20200930_cal.xml" xlink:title="Calculation Links, all" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="ardx-20200930_def.xml" xlink:title="Definition Links, all" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="ardx-20200930_lab.xml" xlink:title="Label Links, all" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
    </appinfo>
  </annotation>
  <import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
  <import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" />
  <import namespace="http://www.xbrl.org/dtr/type/numeric" schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd" />
  <import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <import namespace="http://xbrl.sec.gov/dei/2019-01-31" schemaLocation="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd" />
  <import namespace="http://www.xbrl.org/2009/role/negated" schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" />
  <import namespace="http://fasb.org/us-roles/2019-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2019/elts/us-roles-2019-01-31.xsd" />
  <import namespace="http://fasb.org/us-gaap/2019-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd" />
  <import namespace="http://fasb.org/srt/2019-01-31" schemaLocation="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd" />
  <element name="AvailableForSaleSecuritiesContractualMaturityPeriod" id="ardx_AvailableForSaleSecuritiesContractualMaturityPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element name="CashAndCashEquivalentsGrossUnrealizedGains" id="ardx_CashAndCashEquivalentsGrossUnrealizedGains" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="instant" />
  <element id="ardx_CashCashEquivalentsAndShortTermInvestmentsFairValueDisclosure" name="CashCashEquivalentsAndShortTermInvestmentsFairValueDisclosure" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element name="CashCashEquivalentsAndShortTermInvestmentsGrossUnrealizedGains" id="ardx_CashCashEquivalentsAndShortTermInvestmentsGrossUnrealizedGains" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="instant" />
  <element name="CashCashEquivalentsAndShortTermInvestmentsGrossUnrealizedLosses" id="ardx_CashCashEquivalentsAndShortTermInvestmentsGrossUnrealizedLosses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="debit" xbrli:periodType="instant" />
  <element name="CashCashEquivalentsAndShortTermInvestmentsLineItems" id="ardx_CashCashEquivalentsAndShortTermInvestmentsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="CashCashEquivalentsAndShortTermInvestmentsTable" id="ardx_CashCashEquivalentsAndShortTermInvestmentsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="CommercialPaperCashEquivalentsIncludingSecuritiesMember" id="ardx_CommercialPaperCashEquivalentsIncludingSecuritiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="DomesticCorporateDebtSecuritiesIncludingCashEquivalentsMember" id="ardx_DomesticCorporateDebtSecuritiesIncludingCashEquivalentsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="EmployeeStockPurchasePlanMember" id="ardx_EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element name="LiquidityPolicyTextBlock" id="ardx_LiquidityPolicyTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <element id="ardx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceAndAdditionalDisclosuresAbstract" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceAndAdditionalDisclosuresAbstract" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_PerformanceBasedRestrictedStockUnitsMember" name="PerformanceBasedRestrictedStockUnitsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_ThresholdPercentageOfSalesForTieredRoyalties" name="ThresholdPercentageOfSalesForTieredRoyalties" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_AstrazenecaMember" name="AstrazenecaMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_WarrantTerm" name="WarrantTerm" nillable="true" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_WarrantsExercisedInPeriod" name="WarrantsExercisedInPeriod" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_SolarCapitalAndWesternAllianceBankLoanAgreementMember" name="SolarCapitalAndWesternAllianceBankLoanAgreementMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_PercentageOfReasonablyPossibleIncreaseInRiskAssumption" name="PercentageOfReasonablyPossibleIncreaseInRiskAssumption" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <element id="ardx_PercentageOfReasonablyPossibleDecreaseInRiskAssumption" name="PercentageOfReasonablyPossibleDecreaseInRiskAssumption" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <element id="ardx_IncreaseDecreaseInFinancialInstrumentDueToReasonablyPossibleIncreaseInDesignatedRiskComponent" name="IncreaseDecreaseInFinancialInstrumentDueToReasonablyPossibleIncreaseInDesignatedRiskComponent" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <element id="ardx_IncreaseDecreaseInFinancialInstrumentDueToReasonablyPossibleDecreaseInDesignatedRiskComponent" name="IncreaseDecreaseInFinancialInstrumentDueToReasonablyPossibleDecreaseInDesignatedRiskComponent" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_AtMaturityMember" name="AtMaturityMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_AfterSecondAnniversaryToMaturityDateMember" name="AfterSecondAnniversaryToMaturityDateMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_PercentageOfPremiumPayableOnRedemptionOfTermLoan" name="PercentageOfPremiumPayableOnRedemptionOfTermLoan" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_FeePayableUponClosingOfTermLoan" name="FeePayableUponClosingOfTermLoan" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <element id="ardx_PrepaymentFeePercentage" name="PrepaymentFeePercentage" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <element id="ardx_DefaultInterestRate" name="DefaultInterestRate" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_DebtInstrumentUnaccretedValueFinalFee" name="DebtInstrumentUnaccretedValueFinalFee" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_OtherProductOrServicesRevenueMember" name="OtherProductOrServicesRevenueMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_NoncashInterestExpense" name="NoncashInterestExpense" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_KnightTherapeuticsIncMember" name="KnightTherapeuticsIncMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_CollaborationAndLicensingAgreementsAbstract" name="CollaborationAndLicensingAgreementsAbstract" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_CollaborativeArrangementDevelopmentMilestonesPaymentToBeReceived" name="CollaborativeArrangementDevelopmentMilestonesPaymentToBeReceived" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_CollaborativeArrangementCommercializationMilestonesPaymentToBeReceived" name="CollaborativeArrangementCommercializationMilestonesPaymentToBeReceived" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_CollaborativeArrangementFutureDevelopmentAndCommercializationMilestones" name="CollaborativeArrangementFutureDevelopmentAndCommercializationMilestones" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_DerivativeLiabilityExitFeeMember" name="DerivativeLiabilityExitFeeMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_NonCashLeaseExpense" name="NonCashLeaseExpense" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_CollaborativeArrangementDevelopmentMilestonesPaymentReceived" name="CollaborativeArrangementDevelopmentMilestonesPaymentReceived" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_PercentageOfRoyaltyRevenue" name="PercentageOfRoyaltyRevenue" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_PercentageOfNonRoyaltyRevenue" name="PercentageOfNonRoyaltyRevenue" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_PaymentsOfUnchargedLicenseFees" name="PaymentsOfUnchargedLicenseFees" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" name="ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_IncreaseDecreaseInOperatingLeaseLiabilities" name="IncreaseDecreaseInOperatingLeaseLiabilities" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_IncreaseDecreaseInUnbilledRevenue" name="IncreaseDecreaseInUnbilledRevenue" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_NumberOfPreClinicalStudyReadyCompounds" name="NumberOfPreClinicalStudyReadyCompounds" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_NumberOfCompoundInhibitingFirstUndisclosedTarget" name="NumberOfCompoundInhibitingFirstUndisclosedTarget" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_NumberOfDevelopmentCandidates" name="NumberOfDevelopmentCandidates" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_NumberOfSeparateCollaborativeAgreements" name="NumberOfSeparateCollaborativeAgreements" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_CollaborationAndLicensingAgreementsUpfrontPaymentReceivable" name="CollaborationAndLicensingAgreementsUpfrontPaymentReceivable" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_CollaborationAndLicensingAgreementsUpfrontPaymentReceivableFistInstallment" name="CollaborationAndLicensingAgreementsUpfrontPaymentReceivableFistInstallment" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_TermOfPaymentOfLicenseFeeFirstInstallment" name="TermOfPaymentOfLicenseFeeFirstInstallment" nillable="true" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_CollaborationAndLicensingAgreementsUpfrontPaymentReceivableSecondInstallment" name="CollaborationAndLicensingAgreementsUpfrontPaymentReceivableSecondInstallment" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_TermOfAgreement" name="TermOfAgreement" nillable="true" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_CollaborationAndLicensingAgreementsInitialTransactionPrice" name="CollaborationAndLicensingAgreementsInitialTransactionPrice" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <element id="ardx_TransactionPriceAllocatedToPartiallyUnsatisfiedPerformanceObligations" name="TransactionPriceAllocatedToPartiallyUnsatisfiedPerformanceObligations" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <element id="ardx_CollaborationAndLicensingAgreementsLicenseFee" name="CollaborationAndLicensingAgreementsLicenseFee" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_CollaborationAndLicensingAgreementsSecondMilestonePayment" name="CollaborationAndLicensingAgreementsSecondMilestonePayment" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" name="ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_KyowaKirinCo.LtdMember" name="KyowaKirinCo.LtdMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_CollaborativeDevelopmentMember" name="CollaborativeDevelopmentMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_CostOfRevenueAggregateAmountRecognized" name="CostOfRevenueAggregateAmountRecognized" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="ardx_CollaborationAndLicensingAgreementsPaymentPerTerminationAgreement" name="CollaborationAndLicensingAgreementsPaymentPerTerminationAgreement" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="ardx_ScheduleOfChangesInFairValueTableTextBlock" name="ScheduleOfChangesInFairValueTableTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashReceived" name="ContractWithCustomerLiabilityRevenueRecognizedCashReceived" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashNotYetReceived" name="ContractWithCustomerLiabilityRevenueRecognizedCashNotYetReceived" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_ResearchCollaborationAndOptionAgreementMember" name="ResearchCollaborationAndOptionAgreementMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_RevenueFromContractWithCustomerChangeInEstimate" name="RevenueFromContractWithCustomerChangeInEstimate" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="ardx_LicenseAgreementMember" name="LicenseAgreementMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" name="LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_LicenseAgreementCertainSpecificPatentAndPatentApplicationsMember" name="LicenseAgreementCertainSpecificPatentAndPatentApplicationsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" name="LicenseAgreementDevelopmentCommercializationDistributionInChinaMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" name="LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_XuanzhuHKBiopharmaceuticalLimitedMember" name="XuanzhuHKBiopharmaceuticalLimitedMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_DevelopmentAndCommercializationMember" name="DevelopmentAndCommercializationMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_AtMarketOfferingMember" name="AtMarketOfferingMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_MaximumAggregateOfferingPrice" name="MaximumAggregateOfferingPrice" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <element id="ardx_TimeBasedRestrictedStockUnitsMember" name="TimeBasedRestrictedStockUnitsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="ardx_CommonStockSharesOfferedIssuedOrSold" name="CommonStockSharesOfferedIssuedOrSold" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <element id="ardx_DebtInstrumentAmendmentFeeAmount" name="DebtInstrumentAmendmentFeeAmount" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
</schema>
