<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2004-01-14</periodOfReport>
    <issuer>
        <issuerCik>0000054507</issuerCik>
        <issuerName>WESTAR ENERGY INC /KS</issuerName>
        <issuerTradingSymbol>WR</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001236089</rptOwnerCik>
            <rptOwnerName>RUELLE MARK A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>818 S. KANSAS AVE.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>TOPEKA</rptOwnerCity>
            <rptOwnerState>KS</rptOwnerState>
            <rptOwnerZipCode>66612</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>EVP, CFO</officerTitle></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Common Stock, Par Value $5.00</value></securityTitle><transactionDate><value>2004-01-14</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>F</transactionCode><equitySwapInvolved>0</equitySwapInvolved><footnoteId id="F1"/></transactionCoding><transactionAmounts><transactionShares><value>12806</value></transactionShares><transactionPricePerShare><value>19.91</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>112194</value><footnoteId id="F2"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeTransaction></nonDerivativeTable><footnotes><footnote id="F1">12,806 shares were forfeited for the payment of taxes after 31,250 restricted share units vested and were distributed to the Reporting Person.  The restricted share units were included in the Reporting Person's previously filed Section 16 reports.</footnote><footnote id="F2">Includes 93,750 restricted share units which are subject to forfeiture.</footnote></footnotes><remarks/><ownerSignature><signatureName>Mark A. Ruelle</signatureName><signatureDate>2004-01-15</signatureDate></ownerSignature></ownershipDocument>

