Since the fuel consumption of automobiles increases in proportion to the weight of automobiles, and the emission of exhaust increases in proportion to the amount of fuel consumed, to improve fuel efficiency and reduce exhaust emissions, it is necessary either to develop a highly efficient engine or reduce the weight of the vehicle. In this study, we studied weight reduction using lightweight materials such as aluminum alloys to increase fuel economy. For this purpose, we propose a lightweight design process of the shock tower mounting bracket, which is the largest loaded part among the vehicle parts. The change in strength and dynamic strength was investigated by replacing the existing cast iron material with 320 MPa of aluminum A356 casting material. For strength and dynamic stiffness analysis of the shock tower mounting bracket, the load on the peripheral members was calculated. As a result of the dynamic stiffness analysis, we identified the weak part and calculated that the lifetime of the shock tower mounting bracket is safe for the calculated load conditions. Through this study, we provide a guide for lightweight design and suggest optimal design conditions for development of a vehicle shock tower mounting bracket.