Nowadays the semi-active suspension system is a challenge in the Automobile industry to improve the ride comfort performance of the vehicles. Hence, improving the vehicle ride comfort performance by using the semi-active suspension has a negative effect on the harshness performance of the vehicle. Therefore, this paper suggests a solution to improve the harshness performance of the vehicle through optimizing the damper top mount characteristics of the of the semi-active suspension system. In this study an optimization technique for optimizing the damper top mount characteristics to improve vehicle harshness is developed. The proposed optimization technique employs a new combined objective function based on ride comfort and harshness evaluation. A detailed and accurate damper top mount mathematical model is implemented inside a validated full vehicle model to provide a realistic simulation environment for the optimization study. In order to optimize the damper top mount characteristics for the semi-active suspension system, a Rule-Optimized Fuzzy-Logic controller for semi-active suspension developed and published by the authors in previous papers is used in the study. The ride comfort and harshness of the full vehicle are evaluated by analyzing the body acceleration in different frequency ranges. While, the dynamic stiffness of the damper top mount is used to describe the optimum damper top mount characteristics for different optimization case studies. The results showed that the proposed optimization routine is able to find the optimum characteristics of the damper top mount which can be used with the semi-active suspension system to improve both the harshness and ride comfort performance of the vehicle.