In this chapter, a hybrid active and semi-active seat suspension for heavy-duty vehicles is experimentally investigated to fill the performance gap between the two kinds of seat suspensions. An active actuator with low continuous force output, which is insufficient for an active seat suspension system, is applied together with a semi-active MRF damper. It has several advantages. First, the energy consumption will be less than a merely active seat suspension. Second, the benefits of active and semi-active seat suspension in vibration control will be integrated. The MRF damper can assist the active actuator to suppress the high resonance vibration with low energy consumption, and at the higher frequency (2-4 Hz) vibration, the semiactive seat suspension cannot further improve the seat suspension performance, but the active actuator further reduces the vibration with small force output. Third, it is a fail-safe system because of the semi-active actuator; the failure of the active actuator will have less influence on the system security. Additionally, the low-power active actuator has a small size and a low current requirement which can benefit the installation and application of the hybrid system in an existing semiactive seat suspension. In this study, the proposed hybrid controller only applies measurable variables in practical application.