Abstract: In this paper, the control of a semi-active suspension system using a quarter-car vehicle model was investigated. Due to the presence of nonlinear such as a hardening spring, a magnetorheological damper force in a real suspension system, it is very difficult to achieve desired performances using linear control techniques. To ensure robustness, a Variable Structure Model-following (VSMF) controller has been designed. The controller utilized an optimal control scheme for an active suspension as a reference model. In the controller, the parameters of the switching surface are determined using the method of pole assignment. A rate exponent approach was used to obtain the control law. The efficecy of the scheme was investigated through computer simulation.