A nonlinear control law including an inverse of memoryless nonlinear gain and a sliding mode control with an observer is proposed to stabilise the Hammerstein model system with the parameter uncertainties. The nonlinear inverse gain of a nonlinear system is provided for improving the system performance over the competing designs developed by using the linear assumptions. The sliding mode control is employed to enhance the system performances. The stability of the overall system is assured by a Lyapunov’s direct method including the sliding surface and the error of the state estimate and by a stable sliding surface which is independent of the parameter uncertainties. Finally, the simulations are used to evaluate the validity of the proposed method.