This　paper　proposes　a　novel　approach　to　achieve　self-healing　property　of　cement　sheath　in　the　oil　well　triggered　by　oil　leakage　through　cracks.　An　oil　swellable　polymer　(OSP)　with　oil　absorptivity　as　high　as　700%　was　synthesized　through　emulsion　polymerization.　The　OSP　dispersion　was　added　into　the　Portland　cement　paste.　It　is　found　that　the　oil　absorption　and　the　linear　expansion　of　the　OSP　modified　hardened　cement　paste　(MHCP)　are　greatly　increased　compared　to　the　blank　hardened　cement　paste　(BHCP).　Pore　structure　measurements　by　N-2　adsorption　show　that　the　addition　of　OSP　decreases　the　total　porosity　of　MHCP　which　confirms　that　the　formation　of　the　polymeric　film　in　MHCP.　The　self-healing　ability　of　MHCP　was　evaluated　by　the　oil　flow　test　through　a　single　crack　in　the　cylindrical　specimen.　The　oil　flow　tests　indicate　that　the　leakage　of　oil　through　the　crack　is　gradually　mitigated　due　to　the　expansion　of　the　MHCP　and　thus　the　self-healing　ability　is　successfully　achieved.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.