A new H-infinity/sliding mode controller under a worst-case scenario is described. The controller is designed to solve the problem associated with unmeasurable state variables in the traditional sliding-mode controller, and to improve the time-domain performance under a worst-case scenario. The control input, derived by Lyapunov＇s second method, keeps the system stable. Proof of closed-loop stability is done by an additional form of a sliding surface and an estimation error.