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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-12-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000353567</issuerCik>
        <issuerName>ICO INC</issuerName>
        <issuerTradingSymbol>ICOC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001314421</rptOwnerCik>
            <rptOwnerName>Bristow Derek R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>LOCALITA BREDA LIBERA</rptOwnerStreet1>
            <rptOwnerStreet2>VIA IV NOMVEMBRE 34</rptOwnerStreet2>
            <rptOwnerCity>VEROLANUOVA, BS</rptOwnerCity>
            <rptOwnerState>L6</rptOwnerState>
            <rptOwnerZipCode>25028</rptOwnerZipCode>
            <rptOwnerStateDescription>ITALY</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Group President - Europe</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>36000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>56000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The total includes 56,000 restricted shares of issuer's common stock issued pursuant to the ICO, Inc. 2007 Equity Incentive Plan. 20,000 of these restricted shares will vest on August 13, 2010, and 36,000 of these restricted shares will vest on December 15, 2011, subject to forfeiture prior to vesting in accordance with the terms of the Restricted Stock Agreement pursuant to which such restricted shares were awarded.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Derek R. Bristow</signatureName>
        <signatureDate>2008-12-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
