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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-04-30</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001207183</rptOwnerCik>
            <rptOwnerName>BARMORE GREGORY T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>93 GOVERNOR'S POINT ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HARPSWELL</rptOwnerCity>
            <rptOwnerState>ME</rptOwnerState>
            <rptOwnerZipCode>04079-4339</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-04-30</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>268081</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of in connection with the merger of ICO, Inc. ('ICO') with and into ICO-Schulman, LLC (f/k/a Wildcat Spider, LLC), a wholly-owned subsidiary of A. Schulman, Inc. ('A. Schulman'), which became effective on April 30, 2010 (the 'Effective Date') (the 'Merger'). In accordance with the terms of the Agreement and Plan of Merger, dated December 2, 2009, by and among A. Schulman, ICO and Wildcat-Spider, LLC (the 'Merger Agreement'), each share of ICO common stock held by the reporting person converted into the right to receive approximately (i) $3.64 in cash and (ii) 0.181816 shares of A. Schulman common stock (the 'Merger Consideration').  The closing sale price of A. Schulman common stock on the NASDAQ Global Market on the Effective Date was $26.01.  Accordingly, the value of the Merger Consideration for each share of ICO common stock was approximately $8.37 ($3.64 + $4.73 = $8.37).</footnote>
        <footnote id="F2">Includes 9,000 shares representing former shares of restricted stock that vested immediately prior to the effective time of the Merger and converted into the right to receive the Merger Consideration.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Gregory T. Barmore</signatureName>
        <signatureDate>2010-05-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
