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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-05-11</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>17 - 19 SUPERIOR DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DANDENONG, VICTORIA</rptOwnerCity>
            <rptOwnerState>C3</rptOwnerState>
            <rptOwnerZipCode>3175</rptOwnerZipCode>
            <rptOwnerStateDescription>AUSTRALIA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President - Europe &amp; Asia/Pac</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-05-11</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>21000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>77000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The total includes 77,000 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, 36,000 of these restricted shares will vest on December 15, 2011 and 21,000 restricted shares will vest on May 11, 2012, 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>2009-05-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
