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

    <documentType>4</documentType><periodOfReport>2003-08-25</periodOfReport>
    <issuer>
        <issuerCik>0001008554</issuerCik>
        <issuerName>HUMBOLDT BANCORP</issuerName>
        <issuerTradingSymbol>HBEK</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001196560</rptOwnerCik>
            <rptOwnerName>MOSS KELVIN H</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HUMBOLDT BANCORP</rptOwnerStreet1>
            <rptOwnerStreet2>2998 DOUGLAS BLVD., SUITE 330</rptOwnerStreet2>
            <rptOwnerCity>ROSEVILLE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95661</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Common Stock </value></securityTitle><transactionDate><value>2003-08-25</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>X</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>14908</value></transactionShares><transactionPricePerShare><value>9.47</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>34423</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeTransaction></nonDerivativeTable><derivativeTable><derivativeTransaction><securityTitle><value>Common Stock Warrant (right to buy)</value></securityTitle><conversionOrExercisePrice><value>9.47</value></conversionOrExercisePrice><transactionDate><value>2003-08-25</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>X</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>14908</value></transactionShares><transactionPricePerShare><value>9.47</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2001-06-12</value></exerciseDate><expirationDate><value>2005-06-30</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock </value></underlyingSecurityTitle><underlyingSecurityShares><value>14908</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>9319</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Share Ownership Detail: 25,349 shares held Directly, 9,074 shares held by Kelvin H. Moss TR K &amp; M Profit</footnote></footnotes><remarks/><ownerSignature><signatureName>Kelvin H. Moss</signatureName><signatureDate>2003-08-26</signatureDate></ownerSignature><ownerSignature><signatureName>Signed by Patrick J. Rusnak, Power of Attorney on File</signatureName><signatureDate>2003-08-26</signatureDate></ownerSignature></ownershipDocument>

