In this paper, an experimental study on the dynamic characteristics of a variable damper and the control of a semi-active suspension was performed. The magnitude of damping can be regulated continuously by varying the area of the orifice. The experimental results show that the damping coefficient decreases monotonously as increasing the opening angle and also the damping coefficient increases as the excitation frequency increases. The experimental results from several semi-active suspension systems and conventional system are also compared and discussed. In spite of some crucial limitations (time delay of the actuator, the dependency of the damper on the excitation frequency, and the inherent heavy damping of the system, etc.) the improved performance of the semi-active suspension system was experimentally verified. It was shown that the rms acceleration value of the suspended mass could be reduced to some extent by applying the controllable variable dampers but the peak acceleration could not be reduced satisfactorily due to the inherent limitations.