An engine control system is disclosed in which the air-fuel ratio is controlled by feedback in accordance with the oxygen concentration detected of the exhaust gas, and a feedback control system thereof separate learning compensation values for compensating for the changes of the input/output characteristics of an air flow meter and a fuel injector respectively. The engine control system comprises a device for detecting the engine intake air flow, a device for detecting the engine speed, a device for detecting the oxygen concentration of the exhaust gas, a device for calculating the error between actual and target air-fuel ratios from the oxygen concentration of the exhaust gas, a device for learning the changes in the input/output characteristics of the intake air flow, a detection device to determine a first compensation factor corresponding to the changes in the input/output characteristics thereof, a device for learning the changes in the input/output characteristics of the fuel injection device to determine a second compensation factor corresponding to the changes in the input/output characteristics thereof, a device for calculating a basic fuel injection amount from the first compensation factor, the engine speed and the intake air amount, a device for calculating a required fuel flow rate reducing the air-fuel ratio error from the basic fuel injection amount, the second compensation factor and the air-fuel ratio error, a device for generating a drive signal indicating the required fuel flow rate, and the device for injecting fuel into the intake air path in the engine in response to the drive signal indicating the required fuel flow rate.