An engine control system for a hybrid vehicle having an internal combustion engine and an electric motor as driving force sources, for permitting stopping and starting of the engine in accordance with predetermined drive conditions. The system includes a booster for receiving a negative pressure supplied by an operation of the engine, a pressure detector for detecting a pressure supplied to the brake booster, a throttle-opening state detector for detecting a throttle opening state and an engine-operation enable/disable determining device for determining whether or not to operate the engine when the engine is stopped, based on the throttle opening state detected by the throttle-opening-state detector and the pressure detected by the pressure detector.