This paper presents a nonlinear observer-based control design approach for gasoline engines equipped with exhaust gas recirculation (EGR) system.A mean value engine model is designed for control which includes both the intake manifold and exhaust manifold dynamic focused on gas mass flows.Then,the nonlinear feedback controller based on the developed model is designed for the state tracking control,and the stability of the close loop system is guaranteed by a constructed Lyapunov function.Since the exhaust manifold pressure is usually unmeasurable in the production engines,a nonlinear observer-based feedback controller is proposed by using standard sensors equipped on the engine,and the asymptotic stability of the both observer dynamic system and control dynamic system are guaranteed with Lyapunov design assisted by the detail analysis of the model.The experimental validations show that the observer-based nonlinear feedback controller is able to regulate the intake pressure and exhaust pressure state to the desired values during both the steady-state and transient conditions quickly by only using the standard sensors.