A control system for an internal combustion engine having an intake system and an exhaust system is disclosed. The exhaust system includes a catalyst, and the intake system includes a throttle valve. The engine is mounted on a vehicle having a brake booster to which an intake pressure at downstream of the throttle valve is introduced. The catalyst temperature rise control in which the intake air amount is increased after starting of the engine and the ignition timing is retarded according to a rotational speed of the engine is performed. When a pressure difference between the detected intake pressure and the atmospheric pressure during the catalyst temperature raising control is less than a predetermined pressure, the increased intake air amount and the retard amount of the ignition timing is gradually decreased.