The control objective of an active suspension system is to produce excellent sprung mass isolation (i.e. ride quality), not too large a rattle space and good road holding ability. Due to the specific dynamics, the active suspension usually adopts a compromise control policy such as linear quadratic regulation (LQR) or linear quadratic Gaussian (LQG) to determine the feedback gains of the controller. In contrast to the full-state feedback control, a sliding mode fuzzy control strategy is employed to design a stable controller for a quarter-car model of the active suspension system. Motivated by the principle of singular perturbation, a systematic design approach is introduced and verified by computer simulation. It is shown that satisfactory performance can be achieved even if the system is under perturbed conditions.