A traction control system for a motor vehicle having driving wheels and driven wheels includes a device for detecting the speed of each of the driving wheels of the vehicle, a device for detecting the speed of each of the driven wheels of the vehicle, a device for calculating a slip value of the driving wheels based on the detected speeds of the driving and driven wheels, a traction control device for controlling the driving wheel so that the slip value of each driving wheel is equal to a predetermined desired slip value when the slip value of each driving wheel is greater than the predetermined desired slip value, and a device for estimating a friction coefficient of a road surface which is employed when the predetermined desired slip value is determined. If slip of the driving wheel occurs when the vehicle is started, the estimating device calculates an acceleration of the driving wheel. The friction coefficient of the road surface is estimated based on an engine output when the acceleration of the driving wheel is greater than a predetermined value.