A fuel control system for an internal combustion engine having an intake passage, a compressor provided in the intake passage, a throttle valve disposed downstream of the compressor, a bypass passage connecting an upstream side of the compressor to a downstream side of the compressor, and an air bypass valve provided in the bypass passage. An intake air flow rate of the engine is calculated based on the engine rotational speed and the intake pressure, which are detected when the air bypass valve is determined to be in the opening operation state. An amount of fuel supplied to the engine is then controlled according to the calculated intake air flow rate.