Yaw stability control is an important consideration for improving the stability and handling behavior of a vehicle during extreme steering maneuvers. This paper proposes a fuzzy logic based yaw stability controller for an active front steering of a four-wheeled road vehicle by using steer-by-wire system. The proposed control system takes the yaw rate error, the steering angle given by the driver and the vehicle body side slip angle as inputs, for calculating the additional steering angle as output for stabilizing the yaw moment of the vehicle. A three degrees-of-freedom vehicle model is considered. Performance of the proposed system is simulated for sinusoidal, step maneuver using Matlab/Simulink tool, and the results are compared with the existing fuzzy control system which uses two inputs such steering angle and yaw rate. The simulation results show better performance of the proposed fuzzy based yaw controller as compared with the existing control system.