An abnormality detection system is provided, which detects abnormality in an evaporative fuel control system for an internal combustion engine. A plurality of temperature sensors are arranged in an evaporative fuel storage device at different locations for detecting the temperature of an adsorbent or in the vicinity thereof within the storage device at the different locations. An ECU controls at least one of charging of evaporative fuel from the fuel tank to the storage device and purging of evaporative fuel from the storage device to the intake system of the engine. The ECU determines the presence or absence of an abnormality in the evaporative fuel control system, based upon output values from the temperature sensors assumed when the control system is operative. A state in which adsorption of evaporative fuel generated in the fuel tank to the adsorbent of the storage device has been completed is detected, based upon the amount of a rise in temperature detected while the charging is being effected. The ECU effects the abnormality determination after the state has been detected. The system may be applied to an internal combustion engine in which the air-fuel ratio is controlled by the use of an air-fuel ratio correction coefficient determined in response to an output from an air-fuel ratio sensor.