A control system for an internal combustion engine in which fuel containing alcohol is used. In the control system, a maximum opening of a throttle valve of the engine is set, and a target opening of the throttle valve is set to a value which is equal to or less than the maximum opening. An opening of the throttle valve is controlled so as to coincide with the target opening. The maximum opening is according to a concentration parameter indicative of a concentration of alcohol in the fuel, a temperature parameter indicative of a temperature of the engine, and a number of ignitions performed after start of the engine.