In this paper a novel active suspension scheme that combines sliding mode control with a disturbance observer is proposed for a quarter car model. The disturbance observer estimates the uncertainties in the system and the unknown road disturbance acting on the unsprung mass. Two control strategies to compensate for the uncertainties and the road disturbance in order to improve the ride comfort are proposed. The stability of the suspension system and the disturbance observer is proved. The efficacy of the method is illustrated by simulation for a vehicle suspension system.