The ideal engine mounting system should isolate engine vibration induced by engine disturbing force in the range of engine speed and also prevent engine bounce caused by shock excitation. This implies that the dynamic stiffness and damping properties of an ideal engine mount should be dependent on the frequency and amplitude of the input excitation. Conventional elastomeric mounts don’t meet all the requirements of the ideal design and can only offer a tradeoff between static deflection and vibration isolation, because their dynamic properties is almost constant with the amplitude and frequency of the excitation. Passive hydraulic engine mounts, because of their frequency and amplitude dependent dynamic properties, provide a better performance compared with elastomeric mounts espessialy in low frequency excitation. To solve some problematic aspects of the passive hydraulic mounts and to improve their dynamic performance further, semiactive vibration control techniques have been applied to engine mounting designs. Semiactive mounts can alter their response during operation, i.e., damping and stiffness to some extent.As changes in geometry of the flow paths in real time require rather complex actuation mechanisms to be incorporated in the mount, it is more desirable to be able to change the mount response through changes in the working fluid characteristics. Consequently, semiactive hydraulic mounts have been proposed to use magnetorheological (MR) fluids as the working fluid.In this thesis, firstly the design and modeling of a hydraulic engine mount has been carried out and the simulation of its dynamic behavior has been done considering the governing equations extracted from the mechanical model of the hydraulic engine mount. Finite element analysis using ANSYS has been carried out to calculate parameters of the main rubber of the hydraulic engine mount used in its dynamic behavior simulation. These parameters include static stiffness, volumetric compliance and effective piston area of the main rubber. Then design concept and modeling of a magnetorheological (MR) engine mount has been done. From the mechanical model of the MR mount, its governing equations have been extracted to simulate the dynamic behavior of the mount. Finally, to experimentally evaluate the desined hydraulic and MR engine mounts and their effectiveness, a prototype mount was built and tested. The results of the simulations and tests show the effectiveness of the designed hydraulic and MR engine mounts in vibration isolation and reducing transmissibility at resonant frequency. Keywords: Vibration isolation, Hydraulic engine mount, Semiactive engine mount, Magnetorheological (MR) fluid, Magnetorheological (MR) engine mount