This paper presents a new approach to design a sliding mode controller for a class of mismatched uncertain systems. A method is proposed for the design of a switching surface in the presence of mismatched uncertainties. A design method for a sliding mode observer based on high gain is also proposed in this paper to reconstruct the states of the system for the implementation of sliding mode control. The design technique is simple and computationally efficient. A control problem for the slosh-free motion of a container is considered as the representative of a typical class of systems. A simple pendulum model is considered to represent the lateral slosh. The validity of the proposed scheme is demonstrated by simulation along with the experimental results. © 2009 IEEE.