This paper deals with the static and dynamic performance analysis of an electrohydraulic servoactuator (EHSA) used frequently in helicopter flight control systems. The investigated system is composed of a hydraulic actuator controlled by means of an electrohydraulic servovalve (EHSV). The servovalve includes a jet pipe hydraulic amplifier. The fluid flow characteristics of the jet pipe hydraulic amplifier are known to be extremely complex and do not lend themselves easily to theoretical analysis. Therefore, some published experimental data are used to predict the flow characteristics of this amplifier. A set of nonlinear simultaneous differential equations describing the dynamic behavior of the valve and actuator are derived. These differential equations are used to develop a MATLAB computer simulation program for the studied EHSA. To simplify the simulation, the EHSV model is replaced by a second order transfer function. The static characteristics of the EHSA and its basic elements are measured. The simulation results showed good agreement with the experimental results. The effects of supply pressure and internal leakage in the hydraulic cylinder on the transient response have been investigated theoretically.