In this paper, an adaptive sliding mode controller has been proposed to improve the vehicle yaw stability through an active braking system. Since the vehicles undergo changes in parameters with respect to the wide range of driving condition, such as changing in road friction coefficient and also the dependency of braking forces on this coefficient, an adaptive robust control method is required to guarantee the system stability. So, a two-layer hierarchical control architecture has been designed which in the upper-layer, the value of corrective yaw moment is determined to track the desired vehicle yaw rate and the lower-layer adjust the longitudinal slip of the wheels to its target value. The designed controller, which is insensitive to system uncertainties, offers the adaptive sliding gains to eliminate the bounds of uncertainties. A dynamics vehicle model with seven degrees of freedom and Pacejka non-linear tyre model have been used to computer simulations and evaluated the effect of controller in the step steer input and lane change maneuvers on dry and slippery roads. The simulation results demonstrate the high effectiveness of the proposed controller against the conventional sliding mode controller to improve the vehicle yaw stability in the slippery roads.