An efficient method to determine optimal bushing stiffness for improving noise and vibration of passenger cars is developed. In general, a passenger vehicle includes various bushings to connect body and chassis systems. These bushings control forces transferred between the systems. Noise and vibration of a vehicle are mainly caused by the forces from powertrain (engine and transmission) and road excitation. If bushings transfer less force to the body, levels of noise and vibration will be decreased. In order to manage the forces, bushing stiffness plays an important role. Therefore, it is required to properly design bushing stiffness when developing passenger vehicles.In the development process of a vehicle, bushing stiffness is decided in the early stage (before the test of an actual vehicle) and it is not validated until the test is performed. If it turns out that vehicle performances are not satisfied in the test, another test with bushing changed needs to be conducted, which requires additional costs. Several tests are usually performed to identify bushings which achieve target performances. In addition, the decision of bushing stiffness is complicated since there is typically a conflict between requirements for bushing stiffness from various vehicle performances, such as ride, handling, noise, and vibration. Therefore, in the design stage, the validation of bushing stiffness is desirable to save costs of the vehicle development and ensure the performances of the vehicle.In this paper, a novel optimization methodology based on a numerical approximation model is presented. This method is used to determine optimal stiffness values of bushings in a vehicle for improving the vehicle noise. By using the method, it is found that bushing stiffness is well optimized while reducing the noise.