A slip control system for a motor vehicle controls slippage of driving wheels and includes, a sensor for detecting a slip ratio of each driving wheel, a device for detecting a reduction in speed of each wheel, and a traction control system for decreasing a slip of each driving wheel by controlling brake fluid pressure in each driving wheel so that the slip ratio of each driving wheel is at least equal to a predetermined desired slip ratio when the slip ratio of each driving wheel becomes equal to the desired slip ratio. The system further includes an antiskid brake system for controlling brake fluid pressure, based on the reduction speed of each wheel, so as to cancel a lock condition of the wheel. The antiskid brake system has a first control device for controlling the brake pressure fluid in a condition in which a traction control operation is not carried out by the traction control system, and a second control device for controlling the brake pressure fluid in a condition in which a traction control operation is carried out by the traction control system.