Cloud　service　providers　offer　massive　storage　space　for　individuals　and　enterprises.　To　guarantee　the　integrity　of　outsourced　data,　a　range　of　data　auditing　schemes　have　been　proposed.　The　auditing　tasks　in　these　schemes　are　typically　performed　by　a　Third　Party　Auditor　(TPA)responsible　for　periodically　checking　the　integrity　of　user　data.　However,　such　a　centralized　auditing　framework　is　vulnerable　and　as　a　third　party,　the　auditor　cannot　be　fully　trusted.　In　this　paper,　we　propose　a　decentralized　and　smart　public　auditing　scheme　for　cloud　storage,　which　eliminates　the　involvement　of　the　TPA　and　improves　the　reliability　of　auditing　schemes.　We　build　a　protocol　for　automatic　data　integrity　checking　in　a　decentralized　environment　based　on　a　smart　contract,　which　eliminates　the　involvement　of　data　owners　and　data　users.　Performance　analysis　and　experiments　show　that　our　scheme　is　efficient　and　favorable.