Anti-lock braking system is one of the most important active safety systems used as an essential tool for improving vehicle safety and its passengers during severe braking. One of the main problems in the braking system is the risk of wheels’ locking during braking on the road. And it arises some problems such as increased vehicle stopping distance and reduced handling ability, and it is not suitable in view of vehicle control. The use of anti-lock braking system is one of the most important steps performed for reducing problems and improving the performance of the vehicle brakes. The most effective chassis control system for improving vehicle safety during severe braking is anti-lock braking system (ABS). The basic function of an ABS is to prevent the wheel from locking, and to regulate the longitudinal slip of the wheel at its optimum value in order to generate the maximum braking force. This permits the vehicle to achieve the shortest stopping distance during braking. Extreme nonlinearities and modeling uncertainties existing in vehicle dynamics are the two main difficulties arising in the design of ABS controller. The former is as a result of tire force saturation and the latter is mainly due to variations of road condition and vehicle parameters such as mass and center of gravity of the vehicle. Also, the unmodeled dynamics neglected in the modeling stage together with some practical limitations are considered as the unstructured uncertainties. A suitable controller for the ABS should successfully handle the nonlinearities and uncertainties of the vehicle model. Therefore, to control the system, we require an approach that can make the system robust to uncertainties . In this thesis, a nonlinear optimal controller is analytically designed for ABS by the prediction of the wheel slip response from a continuous nonlinear vehicle dynamics model and is largely robust to system parameters variations by using an auxiliary control signal. Also, it can reduce the vehicle speed at an acceptable speed. A reference model for the wheel slip (which considers the effects of variations of the tire normal load and tire/road condition) is used to be tracked by the controller. The performed analysis along with the simulation results indicate that the designed controller can successfully cope with the strong nonlinearity and uncertainties of vehicle dynamic model. This controller is simulated in the MATLAB/SIMULINK software and the simulation results show that despite various parameters uncertainties, the controller can provide a satisfactory response. Keywords: Anti-lock brake, Longitudinal slip, Stopping distance, Robust control system, Desired slip