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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-09-22</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001167419</issuerCik>
        <issuerName>AspenBio Pharma, Inc.</issuerName>
        <issuerTradingSymbol>apnb</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001363399</rptOwnerCik>
            <rptOwnerName>1837 RMB Managers L.L.C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O RMB CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>10 S. WACKER DR. STE 3210</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001363397</rptOwnerCik>
            <rptOwnerName>1837 Partners L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O RMB CAPITAL MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>10 S. WACKER DR. STE 3210</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>AspenBio Pharma, Inc.</value>
            </securityTitle>
            <transactionDate>
                <value>2006-09-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>300000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.5</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2319325</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This total includes 1,614,260 shares of common stock and 705,065 warrants (rights to buy).</footnote>
        <footnote id="F2">These securities are directly owned by 1837 Partners L.P. and 1837 Partners QP L.P. (&quot;Partnerships&quot;)  As the General Partner to the Partnerships, 1837 RMB Managers L.L.C. may be deemed to be the beneficial owner of the Issuer's securities held by the Partnerships.  1837 RMB Managers L.L.C. disclaims any beneficial ownership of any of the Issuer's securities reported herein for purposes of Rule 16a-1 under the Securities Exchange Act of 1934, as amended, or otherwise, except as to securities representing 1837 Managers L.L.C.'s pro rata interest in the profits of the Partnerships.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Richard M. Burridge, Jr.</signatureName>
        <signatureDate>2006-09-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
