In this paper, a robust adaptive control (RAC) of electro-hydraulic servo-system is investigated. The dynamics of hydraulic systems are highly nonlinear and the system may be subjected to some discontinuous nonlinearities which mostly due to servo-valve characteristics. Aside from the nonlinear nature of hydraulic dynamics, our test bench presents an intermediate interface between the actuator and the servo-valve, which leads to have some pressure drop between the servo-valve and the cylinder chambers. This pressure drop depends on some operating conditions. Therefore, the system may possess both parametric uncertainties and unknown nonlinear functions that may represent modelling errors. To address these challenging issues, the robust adaptive control (RAC) is applied. Based on adaptive update techniques, the parametric uncertainties are compensated. Moreover, a robust method is used to solve the problem derived from the modelling errors. The proposed controller ensure that the position tracking errors of the system remains bounded and can be made arbitrarily small. Simulation studies on the control of hydraulic servo-actuator show the effectiveness of the proposed scheme.