This paper describes the state reconstruction of nonlinear chaotic systems with uncertainty having unknown bounds. The new observer presents simple structures that contain a sliding mode term which is established from the available output measurements. To the best of authors' knowledge, in iteration such classes of observer have not been used in synchronization problem. The convergence of the proposed observer has been proved by Lyapunov inequality equation; LMI; while the performance of the

more »

... tem has been verified by famous chaotic systems such as Lorenz and Rossler. A design procedure for the proposed technique is described and simulation results are presented to show that the proposed chaos observer is vary efficient with regards to the class of chaotic systems.