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

    <documentType>4/A</documentType><periodOfReport>2003-05-08</periodOfReport><dateOfOriginalSubmission>2003-05-09</dateOfOriginalSubmission>
    <issuer>
        <issuerCik>0001065865</issuerCik>
        <issuerName>JANUS CAPITAL GROUP INC</issuerName>
        <issuerTradingSymbol>JNS</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001217498</rptOwnerCik>
            <rptOwnerName>WHISTON MARK B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>JANUS CAPITAL GROUP INC.</rptOwnerStreet1>
            <rptOwnerStreet2>100 FILLMORE STREET</rptOwnerStreet2>
            <rptOwnerCity>DENVER,</rptOwnerCity>
            <rptOwnerState>CO</rptOwnerState>
            <rptOwnerZipCode>80206-4928</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>CEO, Vice Chairman of Board </officerTitle></reportingOwnerRelationship></reportingOwner><derivativeTable><derivativeTransaction><securityTitle><value>Option (Right to Buy) and LSAR</value><footnoteId id="F1"/><footnoteId id="F2"/></securityTitle><conversionOrExercisePrice><value>14.37</value><footnoteId id="F1"/></conversionOrExercisePrice><transactionDate><value>2003-05-08</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>32255</value></transactionShares><transactionPricePerShare><footnoteId id="F4"/></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><footnoteId id="F3"/></exerciseDate><expirationDate><value>2013-05-07</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>32255</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>32255</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Transaction previously reported.  Amendment to report the correct exercise price.</footnote><footnote id="F2">Limited Stock Appreciation Rights (&quot;LSARs&quot;) are granted in tandem with stock options.  LSARs are automatically exercised (in lieu of related options) upon a change-of-control of the Company which has not been approved by certain members of the Company's board of directors and result in the receipt of only cash by the option holder.  LSARs terminate when the related options are exercised or terminated.</footnote><footnote id="F3">The option award vests annually in five equal installments beginning on May 8, 2004.</footnote><footnote id="F4">There is no price for this derivative security.</footnote></footnotes><remarks/><ownerSignature><signatureName>Jill M. Jepson, Attorney-in-Fact for Mark B. Whiston</signatureName><signatureDate>2004-01-02</signatureDate></ownerSignature></ownershipDocument>

