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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-07-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000722830</issuerCik>
        <issuerName>IMMUNOMEDICS INC</issuerName>
        <issuerTradingSymbol>IMMU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001029578</rptOwnerCik>
            <rptOwnerName>GOLDENBERG DAVID M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O IMMUNOMEDICS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>300 AMERICAN ROAD</rptOwnerStreet2>
            <rptOwnerCity>MORRIS PLAINS</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07950</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CSO &amp; Chairman of the BOD</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Rights</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-07-14</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1500000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-07-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.01 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1500000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1500000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each performance right represents a contingent right to receive one share of Immunomedics, Inc. common stock.  The performance rights will vest  (i) as to 500,000 shares (a) on or after the third anniversary of the grant date and (b) upon Immunomedics, Inc. common stock achieving a fair market value of $7.35 or higher based on the average closing price for the prior 30 consecutive trading days;  (ii) as to 500,000 shares (a) on or after the third anniversary of the grant date and (b) upon Immunomedics, Inc. common stock achieving a fair market value of $11.00 or higher based on the average closing price for the prior 30 consecutive trading days; and (iii) as to 500,000 shares (a) on or after the third anniversary of the grant date and (b) upon Immunomedics, Inc. common stock achieving a fair market value of $15.00 or higher based on the average closing price for  the prior 30 consecutive trading days.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ David M. Goldenberg</signatureName>
        <signatureDate>2015-07-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
