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

<documentType>4</documentType><periodOfReport>2003-05-16</periodOfReport>
<issuer><issuerCik>0000830257</issuerCik>
        <issuerName>BSB BANCORP INC</issuerName>
<issuerTradingSymbol>BSBN</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001083336</rptOwnerCik>
            <rptOwnerName>DECKER REXFORD C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
<reportingOwnerRelationship>
<isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>Senior VP and CFO</officerTitle></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-05-16</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>2250</value></transactionShares><transactionValue><value>10.1666</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>11428</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value>Jt. Ten w/ Spouse</value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><derivativeSecurity><securityTitle><value>Incentive Stock Option-Right-to-Buy</value></securityTitle><conversionOrExercisePrice><value>10.1666</value></conversionOrExercisePrice><transactionDate><value>2003-05-16</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>2250</value></transactionShares><transactionValue><value>0</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>1995-03-28</value><footnoteId id="F2"/></exerciseDate><expirationDate><value>2004-03-28</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common</value></underlyingSecurityTitle><underlyingSecurityShares><value>2250</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>0</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeSecurity><footnotes><footnote id="F1">Individual also reports direct holdings of 300 shares  held individually,  298 shares held individually in 401(k) Plan account, and indirect holdings of 300 shares held as custodian for each of two sons.</footnote><footnote id="F2">Option subject to vesting at 25% of total annually beginning 3/28/95.</footnote></footnotes><ownerSignature><signatureName>Larry G. Denniston, Attorney-in-fact</signatureName><signatureDate>2003-05-16</signatureDate></ownerSignature></ownershipDocument>

