It is possible to improve vehicle vibration by tuning the parameters of engine mounting system. By optimization of mount characteristics or finding the optimal position of mounts, vibration of the engine and transmitted force from the engine to the chassis can be reduced. This paper examines the optimization of 6-degree-of-freedom engine mounting system based on torque roll axis (TRA) mode decoupling, so that TRA direction coincides with one of the natural modes of vibration. This is achieved by determination of optimal location and stiffness of mounts. In order to find feasible results, physical constraints are taken into account in optimization process. A detailed procedure of optimization problem is explained. Finally, by comparing the frequency and time responses of the optimal design with the original configuration, it is concluded that TRA decoupling is a proper objective function in engine mounting optimization and can greatly improve the vibration behavior of the engine. Achieving decoupled system, the optimal configuration has a better chance of placing dominant natural frequency below the operation range. Also, the forces transmitted through the mounts are reduced noticeably in the optimal design.