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

    <documentType>4/A</documentType><periodOfReport>2003-10-13</periodOfReport><dateOfOriginalSubmission>2003-10-13</dateOfOriginalSubmission>
    <issuer>
        <issuerCik>0001008554</issuerCik>
        <issuerName>HUMBOLDT BANCORP</issuerName>
        <issuerTradingSymbol>HBEK</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001102039</rptOwnerCik>
            <rptOwnerName>MASON THEODORE S</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>2003-10-13</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>3000</value><footnoteId id="F1"/></transactionShares><transactionPricePerShare><value>16.0063</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>54624</value><footnoteId id="F2"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeTransaction></nonDerivativeTable><footnotes><footnote id="F1">Open market sale pursuant to Trading Plan (10b-5) effective August 27, 2003. </footnote><footnote id="F2">Ownership of common stock is as follows: 54,334 held Direct, 290 held by Immediate Family Member. </footnote></footnotes><remarks/><ownerSignature><signatureName>Theodore S. Mason</signatureName><signatureDate>2003-10-14</signatureDate></ownerSignature><ownerSignature><signatureName>Signed by Patrick J. Rusnak, Power of Attorney on File. </signatureName><signatureDate>2003-10-14</signatureDate></ownerSignature></ownershipDocument>

