Abstract: An observer design method is proposed for a class of time-delay nonlinear systems. The observer design for the systems without external disturbance is considered first and then the systems with uncertain external disturbance. The delay-time is entirely owing to time variation, and the disturbance is composed of two parts, i.e., a nonlinear term which is assumed to satisfy global Lipschitiz conditions and an uncertain bounded term. The sliding mode theory is applied to stabilizing the error estimation system, based on Lyapunov stability theory. Then, the stability problem can be transferred into the solution to a class of linear matrix inequalities. A simulation example is given to illustrate the feasibility of the presented method.