Abstract. This paper investigates the problem of observer-based robust mixed H 2 /H ∞ control for a class of autonomous spacecraft rendezvous systems. The model of system is based on Clohessy-Wiltshire (C-W) equations, which contain non-circle uncertainty (NCU) of target track, white noise and bounded energy noise. Considering the unobservable states of system, the paper uses state-observer to implement state feedback control and separates the stateobserver subsystem from the state-feedback subsystem with several sets of separated-parameters to reduce the complexity of derivation. In this paper, the aim of the control problem is to design a state-observer and a state feedback controller such that the closed-loop poles of two subsystems are placed within a given disc, the H ∞ norm of the transfer function from the bounded energy noise to output and the H 2 norm from the white noise to output is guaranteed to be less than two preset level. With Lyapunov theory, the observer and controller design problem can be transferred into solving a group of linear matrix inequalities (LMIs). An illustrative example is given to show the effectiveness of the proposed observer and the controller design approach.