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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2022-05-10T15:31:09.0473385+00:00 -->
<!-- Version            : 5.0.1.747 -->
<!-- Package ID         : 4186adcdf10c4ba9b76bd7bb5cd3a8b0 -->
<!-- Copyright (c) 2022 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="arwr_LeasePaymentsCommencementDate" name="LeasePaymentsCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="arwr_PaymentsOfLeaseholdImprovementsNetOfTenantImprovementAllowances" name="PaymentsOfLeaseholdImprovementsNetOfTenantImprovementAllowances" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_NumberOfOptionsToRenew" name="NumberOfOptionsToRenew" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="arwr_LeaseExpansionExpirationMonthAndYear" name="LeaseExpansionExpirationMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="arwr_LeaseExpansionCommencementMonthAndYear" name="LeaseExpansionCommencementMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="arwr_CorporateHeadquartersInPasadenaMember" name="CorporateHeadquartersInPasadenaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_ColoradoOwnerLLCMember" name="ColoradoOwnerLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_ResearchFacilityInMadisonMember" name="ResearchFacilityInMadisonMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_HalozymeIncMember" name="HalozymeIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_SubleaseAgreementMember" name="SubleaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_AdditionalLandSubjectToLease" name="AdditionalLandSubjectToLease" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="arwr_ExpectedPaymentsOfLeaseholdImprovementsNetOfTenantImprovementAllowances" name="ExpectedPaymentsOfLeaseholdImprovementsNetOfTenantImprovementAllowances" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_SubleaseCommencementDate" name="SubleaseCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="arwr_EstimatedPaymentsForOperatingExpensesYearOne" name="EstimatedPaymentsForOperatingExpensesYearOne" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="arwr_TwoThousandsFourEquityIncentivePlanMember" name="TwoThousandsFourEquityIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_TwoThousandsThirteenIncentivePlanMember" name="TwoThousandsThirteenIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_OutsideOfEquityCompensationPlansMember" name="OutsideOfEquityCompensationPlansMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_TwoThousandTwentyOneIncentivePlanMember" name="TwoThousandTwentyOneIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="arwr_GrantDateFairValueOfOptionsGrantedDuringPeriod" name="GrantDateFairValueOfOptionsGrantedDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_GrantDateFairValueOfOtherThanOptionsGrantedDuringPeriod" name="GrantDateFairValueOfOtherThanOptionsGrantedDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_CommercialNotes" name="CommercialNotes" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_HeldToMaturitySecuritiesFairValueNonCurrent" name="HeldToMaturitySecuritiesFairValueNonCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="arwr_CertificateOfDeposits" name="CertificateOfDeposits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
</xsd:schema>
