A driving wheel slip control system for a vehicle detects an excessive slip state of at least one of the driving wheels of the vehicle and reduces engine output when the excessive slip state is detected, by repeating alternate fuel cut and fuel supply such that fuel supply is stopped for a first predetermined time period, and a second predetermined time period. During the second predetermined time period the engine is supplied with an amount of fuel smaller than one required for an operating condition of the engine in the excessive slip state. If the excessive slip state has a greater variation in magnitude than a certain value, fuel supply is continuously effected for a third predetermined time period longer than the first predetermined time period or all the time during the excessive slip state. In another embodiment, slip value is determined which corresponds to the degree of an excessive slip of the driving wheel and a supply controller controls the amount of fuel supplied to various engine cylinders depending on the slip value. A fuel cut-off control cuts off the fuel supply to the various cylinders the number of which depends on the slip value when the slip value exceeds a predetermined slip value.