The paper investigates the change of frequency response characteristics on two-stage gear reduction servo system according to the variation of backlash amount of each gear reduction stage, under the condition that the backlash of total system is constant. It is shown that the frequency response characteristics of the system heavily depend on the contribution ratio which is defined as a ratio of the first backlash amount to the total backlash. It is also found that there is an optimal backlash combination to maximize the bandwidth of two-stage gear reduction servo system when the allowable total backlash is determined.