Category (3). This paper shows the validation of gear damage mathematical modeling using mechanical vibration analysis. It shows how the gear failures are simulated in MATLAB environment and compared with the mechanical vibrations signals taken from a two-steps gear casing test bed. In comparison, spectral analysis is realized. The first part of the paper presents the mathematical modeling of gear failure, the second part shows the experimental assembly and the data adquisition system. The third part explains different signal processing techniques for comparison and model validation. Commercial processing of mechanical vibrations and the spectral analysis accomplished in this study is also explained. And, finally, the results of such comparison, conclusions and recommendations are shown.