<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-11-17</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000704384</issuerCik>
        <issuerName>BIOVEST INTERNATIONAL INC</issuerName>
        <issuerTradingSymbol>BVTI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001189294</rptOwnerCik>
            <rptOwnerName>LAURUS MASTER FUND LTD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001465346</rptOwnerCik>
            <rptOwnerName>PSource Structured Debt Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001296341</rptOwnerCik>
            <rptOwnerName>LAURUS CAPITAL MANAGEMENT LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001413180</rptOwnerCik>
            <rptOwnerName>Valens U.S. SPV I, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001420984</rptOwnerCik>
            <rptOwnerName>Valens Offshore SPV I, Ltd.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001413179</rptOwnerCik>
            <rptOwnerName>Valens Capital Management, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001296339</rptOwnerCik>
            <rptOwnerName>GRIN DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001296338</rptOwnerCik>
            <rptOwnerName>GRIN EUGENE</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LAURUS CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>875 THIRD AVENUE, 3RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Disclaimed Group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.01 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14834782</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On November 11, 2010, Biovest International, Inc., a Delaware corporation (the &quot;Company&quot;), and its subsidiaries (collectively, the &quot;Debtors&quot;) emerged from Chapter 11 protection under the U.S. Bankruptcy Code pursuant to the Debtors' First Amended Joint Plan of Reorganization (as modified by the First Modification to the First Amended Joint Plan of Reorganization, the &quot;Plan&quot;), which was confirmed by order of the U.S. Bankruptcy Court for the Middle District of Florida, Tampa Division, on November 2, 2010 and became effective as of November 11, 2010.  (Continued in Footnote 2)</footnote>
        <footnote id="F2">Upon effectiveness of the Plan, the Company issued a total of 14,834,782 shares (the &quot;Shares&quot;) of its common stock, par value $0.01 per share, to Laurus Master Fund, Ltd. (In Liquidation), a Cayman Islands company (the &quot;Fund&quot;), PSource Structured Debt Limited, a Guernsey company (&quot;PSource&quot;), Valens U.S. SPV I, LLC, a Delaware limited liability company (&quot;Valens US&quot;), and Valens Offshore SPV I, Ltd., a Cayman Islands company (&quot;Valens Offshore&quot; and, collectively with the Fund, PSource and Valens US, the &quot;Investors&quot;).  (Continued in Footnote 3)</footnote>
        <footnote id="F3">The Shares issued to the Investors consist of:  (i) 4,599,927 Shares issued to PSource; (ii) 1,036,468 Shares issued to Valens US; (iii) 7,320,877 Shares issued to Valens Offshore; and (iv) 1,877,510 Shares issued to the Fund.  The Fund is in liquidation under the supervision of the Grand Court of the Cayman Islands.  The Joint Official Liquidators (&quot;JOLs&quot;) are Chris Johnson and Russell Smith of Johnson Smith Associates, Ltd.  The JOLs have discretion over the management of the Fund and the disposition of its assets, including the securities owned by the Fund reported in this statement.  (Continued in Footnote 4)</footnote>
        <footnote id="F4">Laurus Capital Management, LLC (&quot;LCM&quot;), acting through its controlling principals, Eugene Grin and David Grin, provides day-to-day investment management services to the Fund and its two feeder funds concerning their respective assets, including the securities owned by the Fund reported in this statement, subject to certain oversight and preapproval rights of the JOLs and LCM's obligations to the Fund under the Seventh Amended and Restated Investment Management Agreement dated as of April 26, 2007, as amended, restated, modified and/or supplemented from time to time; all of the foregoing are subject to specific directions otherwise given by the JOLs at their discretion.  (Continued in Footnote 5)</footnote>
        <footnote id="F5">PSource is managed by LCM, subject to certain preapproval rights of the board of directors of PSource.  Valens US and Valens Offshore are managed by Valens Capital Management, LLC (&quot;VCM&quot;).  Eugene Grin and David Grin, through other entities, are the controlling principals of LCM and VCM and share voting and investment power over the securities owned by the Fund (subject to the oversight and preapproval rights of the JOLs), PSource, Valens US and Valens Offshore reported in this statement.  The JOLs share voting and investment power over the securities owned by the Fund.  Each of the JOLs, LCM, VCM, Eugene Grin and David Grin disclaims beneficial ownership of the securities held by the Investors except to the extent of such person's pecuniary interest in the Investors, if any.  (Continued in Footnote 6)</footnote>
        <footnote id="F6">The filing of this statement shall not be deemed an admission that any person is, for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise, the beneficial owner of any equity securities covered by or described in this statement.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>By:  /s/ Russell Smith, Joint Official Liquidator (for the account of Laurus Master Fund, Ltd. (In Liquidation) and with no personal liability)</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin, Authorized Signatory of PSource Structured Debt Limited</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin, Authorized Signatory of Laurus Capital Management, LLC</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin, Authorized Signatory of Valens U.S. SPV I, LLC</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin, Authorized Signatory of Valens Offshore SPV I, Ltd.</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin, Authorized Signatory of Valens Capital Management, LLC</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ David Grin</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>By:  /s/ Eugene Grin</signatureName>
        <signatureDate>2011-02-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
