Building　relationships　with　external　stakeholders　is　essential　for　business　success.　The　existing　literature　mentions　how　relationship　building　affects　financial　decisions,　while　the　impact　of　political　relationship　building　on　market　efficiency　is　unclear.　This　paper　employs　the　difference-in-differences　approach　(DID)　to　investigate　whether　and　how　interruptions　in　political　relationship　building　with　government　officials　may　affect　market　efficiency　using　China＇s　anti-corruption　campaign　in　2012　as　a　quasi-natural　experiment.　The　study　finds　that　interruptions　in　political　relationship　building　caused　by　the　anti-corruption　campaign　would　enhance　market　efficiency　by　increasing　information　quality　and　reducing　noise　trading.　Cross-sectional　tests　show　that　the　effect　is　more　pronounced　in　firms　with　higher　information　transparency　and　lower　noise　trading.　This　study　enriches　the　literature　on　corporate　political　relationship　building　and　provides　a　new　interpretation　of　market　efficiency　in　emerging　markets　in　terms　of　irrational　trading.