Abstract: One tooth broke after the gear component had worked for 500 hours. In order to find out the failure mode and cause, macro and micro observation, EDS analysis, microstructure examination, chemical composition analysis, hardness testing, and surface roughness analysis were carried out. In addition, the production processing was analyzed. The results show that the fracture mode of the tooth is fatigue fracture. The fatigue failure was mainly caused by inlaid matter from grinding by grinding wheel. In order to prevent such failure, it is advised that the feed amount of grinding should be reduced and proper coolant should be used. In addition, visual inspection should be carried out with multiplying glass or stereoscopic microscope.