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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2018-02-01</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001158041</issuerCik>
        <issuerName>TURQUOISE HILL RESOURCES LTD.</issuerName>
        <issuerTradingSymbol>TRQ</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001608904</rptOwnerCik>
            <rptOwnerName>SailingStone Capital Partners LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE CALIFORNIA STREET</rptOwnerStreet1>
            <rptOwnerStreet2>30TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94111</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001685655</rptOwnerCik>
            <rptOwnerName>SailingStone Holdings LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE CALIFORNIA STREET</rptOwnerStreet1>
            <rptOwnerStreet2>30TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94111</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001685657</rptOwnerCik>
            <rptOwnerName>Davis MacKenzie B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE CALIFORNIA STREET</rptOwnerStreet1>
            <rptOwnerStreet2>30TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94111</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001685658</rptOwnerCik>
            <rptOwnerName>Settles Kenneth L Jr</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE CALIFORNIA STREET</rptOwnerStreet1>
            <rptOwnerStreet2>30TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94111</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>422933</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Held by SailingStone Global Natural Resources Fund, L.P.</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Kenneth Settles holds approximately 0.89% of the limited partnership interests of SailingStone Global Natural Resources Fund, L.P. (the &quot;Fund&quot;), and may be considered to have a pecuniary interest in the proportionate amount of the common stock of the Company held by the Fund, or 188,205 shares.  MacKenzie Davis holds approximately 1.11% of the limited partnership interests of the Fund and may be considered to have a pecuniary interest in the proportionate amount of the common stock of the Company held by the Fund or 234,728 shares.</footnote>
        <footnote id="F2">Each of the Reporting Persons (other than Kenneth Settles and MacKenzie Davis to the extent set forth above), hereby disclaims beneficial ownership of the shares held by the Fund pursuant to Rule 16a-1(a)(4) under the 1934, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of any of the reported shares for purposes of Section 16 or for any other purpose.</footnote>
    </footnotes>

    <remarks>On February 1, 2018, the Reporting Persons took one or more actions which could be deemed have the purpose or effect of influencing or changing the control of Turquoise Hill Resources Ltd. (the &quot;Company&quot;).  Prior to this date, for the purposes of Section 16 of the Securities Exchange Act of 1934, as amended (the &quot;1934 Act&quot;), the Reporting Persons did not beneficially own more than 10% of any class of the Company's equity securities due to exemptions from beneficial ownership under Rule 16a-1(a)(1)(v) and  Rule 16a-1(a)(1)(vii) under the 1934 Act, as applicable, for shares of the Company held in accounts for which SailingStone Capital Partners LLC serves as investment adviser.

File three copies of this Form, one of which must be manually signed. If space is insufficient, See Instruction 6 for procedure. Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.</remarks>

    <ownerSignature>
        <signatureName>/s/ Patrick W.D. Turley, Attorney-in-Fact</signatureName>
        <signatureDate>2018-02-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
