In this paper, a sampled data's observer for states and disturbance estimations is proposed for Electro-Hydraulic-Actuator (EHA) systems. The proposed observer is characterized by two main features. The first one is a time varying correction gain which tends to augment the sampling periods for the acquisition of the output measured variable of the EHA system. The second one is its ability to reduce the noise measurements effects on the performances of the observer. The convergence of the proposed observer is proved using Lyapunov function and small gain arguments. A theoretical expression of the maximum allowable sampling period T_max for the acquisition of the measured output of the EHA system is also derived. Simulation results on a validated model of the EHA systems shows the effectiveness of our proposed observer for the application to the EHA systems.