A slip control system for a vehicle having a differential which distributes engine output to left and right driving wheels suppresses the engine output when the slip of at least one of the driving wheels exceeds a first threshold value. Slips of the left and right driving wheels are periodically detected, and a spin pattern of the driving wheels is periodically determined on the basis of the slips of the left and right driving wheels. Whether the vehicle is running on a split surface road, where the parts of the road surface in contact with the left and right driving wheels have different friction coefficients, is determined on the basis of the present spin pattern and the preceding spin pattern according to a predetermined split surface determining rule. When it is determined that the vehicle is running on a split surface road, the first threshold value is increased.