A control system for an internal combustion engine having a throttle valve disposed in an intake passage of the engine. A target intake air amount of the engine is calculated, and an intake pressure of the engine is estimated. A wide-open intake air amount is calculated according to the engine rotational speed, and a theoretical intake air amount is calculated according to the wide-open intake air amount and the intake pressure. The wide-open intake air amount is an intake air amount corresponding to a state where the throttle valve is fully opened, and the theoretical intake air amount is an intake air amount corresponding to a state where no exhaust gas of the engine is recirculated to a combustion chamber of the engine. further, an exhaust gas recirculation ratio is calculated using the theoretical intake air amount and the target intake air amount, and a target output torque of the engine is calculated using the target intake air amount and the exhaust gas recirculation ratio. The engine is controlled using the target output torque.