Advanced vehicular technologies have been increasingly popular since they improve fuel economy. Automobiles with variable cylinder management are capable of turning on/off the cylinders in order to optimize the fuel consumption. Hybrid vehicles such as hybrid electric vehicles (HEVs) or hydraulic hybrid vehicles (HHVs) allow the engines to operate in the most efficient region. Besides, the hybrid technology includes capturing the braking energy, otherwise wasted as heat, to aid the acceleration. However, the enhancement in fuel efficiency comes with unbalance, shock and wider range of frequency vibration. Noise and vibration is actually one of the main obstacles in commercializing the HHV technology. This study is to design a vibration isolator to work for HHVs effectively and economically. The vibration profile of HHVs is proven to include both shock load at the switches of power sources and wide frequency range of vibration. That the HHVs engine is turned on/off frequently and the hydraulic pumps/motors operate between 0 and 2000RPM, corresponding to 0-300Hz, poses difficult challenges for the isolation system. Rubber mounts are cheap, but only good for static load support and suitable for low power engine. Passive hydraulic mounts are only effective for conventional engines with unvarying working schedules. On the other hand, the active mounts are responsive for any condition, but too costly for commercial vehicles. Semi-active mounts with magnetorheological fluid (MRF) have been researched and recognized as a highly potential solution for hydraulic hybrid vehicles. The semi-active MRF mount is constructed very similar to a conventional hydraulic mount. However, the working fluid is an MRF which can quickly change its characteristics when the magnetic field is present. The main features of the MRF mount include multiple controllable MR valves, utilizing the flow (valve) mode, to connect the top and bottom fluid chambers. In addition, the mount is also capable of employing the fluid in squeeze mode. The structure of the MRF mount allows the stiffness and damping to be controlled in real time. The controllability makes the mount tunable to particularly fit the requirements of the HHVs. In this study, a mathematical model was constructed to predict the performance of the mount. The parameters were tuned so that the mount is effective within the whole operating frequency range of the HHVs vibration.