A control system for an internal combustion engine is disclosed. The engine has an exhaust gas recirculation device which includes an exhaust gas recirculation passage for recirculating exhaust gases from the engine to an intake system of the engine, and an exhaust gas recirculation control valve provided in the exhaust gas recirculation passage, for controlling a flow rate of the exhaust gases. An air-fuel ratio control amount is calculated based on an output of the air-fuel ratio sensor provided in the exhaust system of the engine. The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled with the air-fuel ratio control amount. A failure of the exhaust gas recirculation device is determined based on a changing component of the air-fuel ratio control amount when changing an opening of the exhaust gas recirculation control valve in a predetermined cycle.