One of the most significant factors affecting the cost of a gearbox is its mass, which can be changed by optimizing the gearbox ratios. Accordingly, to achieve the minimal mass of a gearbox, an optimization is needed for the partial gear ratios. The present study is aimed to minimize the mass of Two-stage Helical Gearboxes with First Stage Double Gear-sets via optimizing the second partial gear ratios. Several input factors are employed for the exploration of their effects on the optimum gear ratio of the second stage. An experimental simulation is created with the computer assistance to obtain a regression equation which then can help predict the results. The input factors and their interactions have been found to have great impacts on the response. Noticeably, the predicted values are consistent with the experiment results.