A fuel supply control system performs asynchronous fuel injection in response to acceleration demand for injecting a controlled amount of fuel irrespective of an engine revolution cycle. The amount of fuel for asynchronous injection in an engine transition state from engine decelerating state, in which fuel cut-off is performed, to engine acceleration state, is determined on the basis of a set value which is a latched fuel injection upon initiation of fuel cut-off operation, and an instantaneous fuel injection amount derived on the basis of the instantaneous fuel injection control parameters. The set value is modified in relation to an amount of fuel left on a periphery of an induction system.