A control system of an engine in which a purge gas containing evaporated fuel desorbed from a canister is supplied to an intake passage of the engine is provided. The control system includes a deceleration fuel cutoff module for performing a deceleration fuel cutoff to stop a fuel supply from an injector to the engine when a predetermined deceleration fuel cutoff condition is satisfied in a decelerating state of the engine, a purge unit for purging by supplying the purge gas to the intake passage during the deceleration fuel cutoff, an O2 sensor provided in an exhaust passage of the engine, an abnormality determining module for determining an abnormality of the O2 sensor based on a change of an output value of the O2 sensor that is caused by the deceleration fuel cutoff, and a purge restricting module for restricting the purge during the abnormality determination.