This paper presents an optimization of a four-degrees-of-freedom vehicle?s human with seat suspension system using genetic algorithms (GA) to determine vehicle suspension parameters to achieve the best comfort of the human. Maximum allowed vertical acceleration of the human body and the suspension working space were used as constrained limits in this study. The genetic algorithm is applied to solve the optimization problem. The optimization results are compared through step and sinusoidal excitation of the seat suspension system for the optimal and currently used suspension systems. In case of sinusoidal profile excitation, results showed that RMS acceleration of the driver, seat suspension working space and sprung mass are reduced by about 21%, 21.5% and 20.3%, respectively. At step profile excitation, RMS acceleration of the driver, seat suspension working space and sprung mass are reduced by about 24%, 24.98% and 7.15%, respectively. The optimal design parameters of the suspension systems obtained are ks= 10039 N/m and cs= 900 N.s/m in case of sinusoidal input and ks= 10030 N/m and cs= 913 N.s/m in case of step input, respectively.