A hydraulic anti-lock brake system for a motor vehicle including a detector for obtaining rotating speeds of front right and left wheels and rear right and left wheels of the vehicle, hydraulic brakes for braking the front and rear wheels with brake pressures, and an anti-lock pressure regulating device for controlling the brake pressures on the basis of an output of the detector, so as to prevent excessive slipping of the front and rear wheels, the anti-lock pressure regulating device including a device for generating a pressure difference between the brake pressures for the rear right and left wheels, such that the brake pressure for the higher-speed rear wheel is lower than that for the lower-speed rear wheel, so that the higher-speed rear wheel is used as a speed monitoring wheel whose speed is used by the pressure regulating device for control the brake pressures.