In this study, a new controllable engine mounting system for vibration control of passenger vehicles is proposed. The proposed mounting system consists of two smart material actuators: a piezostack actuator and a magnetorheological-fluid actuator. First, the dynamic responses of an in-line four-cylinder engine supported by three rubber mounts are mathematically analysed by considering the six-degree-of-freedom motion of the engine body, whose excitation is generated by the inner forces during the engine combustion process. Second, the proper positions of the two actuators are determined. Two magnetorheological mounts are used as roll mounts, and one piezostack mount is used as the right-hand mount, in order to reduce the unwanted engine vibration in a broadband frequency range. Third, the piezostack mount and the magnetorheological mount are designed and manufactured, followed by installation in the engine mounting system. Subsequently, for effective vibration isolation, a sliding-mode controller, which is robust to disturbances and system uncertainties, is designed. Finally, in order to demonstrate the effectiveness of the proposed new engine mounting system, vibration control performances are evaluated by adopting the hardware-in-the-loop simulation test method associated with the sliding-mode controller. The vibration control responses are presented at various engine operating speeds in the time domain and the frequency domain. It was found that the vibration control performance is improved by 30% at an engine speed of 750 r/min and by 17% at an engine speed of 2000 r/min using the proposed engine mounting system associated with the controllers.