<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>3</documentType><periodOfReport>2003-06-25</periodOfReport>
    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000054507</issuerCik>
        <issuerName>WESTAR ENERGY INC /KS</issuerName>
        <issuerTradingSymbol>WR</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001225062</rptOwnerCik>
            <rptOwnerName>CARTER MOLLIE H</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>Common Stock, Par Value $5.00</value></securityTitle><transactionAmounts><transactionShares><value>0</value></transactionShares></transactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><footnotes/><ownerSignature><signatureName>Cynthia S. Couch by power of attorney</signatureName><signatureDate>2003-06-27</signatureDate></ownerSignature></ownershipDocument>

