Abstarct: This thesis presents a new High-order sliding mode control baxsed on observer for active suspension system. First of all, the state-space model of system is defined and all the dynamics are considered as lumped uncertainties. Then, a seconde-order sliding mode controller is designed. Since the dynamics of system has been regarded as unknown term, a super-twisting disturbance observer is developed and the second-order sliding mode controller baxsed on disturbance observer is formed. The proposed control law can overcome to the various uncertainties such as parametric uncertainty, external disturbance and un-modeled dynamics. The chaterring phenomenon has been attenuated through the proposed control method. In addition, a sliding-model controller baxsed on disturbance observer is designed for comparison. The robustness behavior, valid control effort, driver comfort and minimization of the displacement are the features of the proposed control scheme. The stability of the closed-loop system is guaranteed via Lyapunov function. The simulation is accomplished for passive suspension system and the active suspension systems. The simulation results demonstrate on the effectiveness of the proposed control law in comparison with the conventional approach. Matlab software is utilized for simulation.