The main aim of this article is study the cause of gear wheel failure. This component has worked in the motorcycle gearbox. During the operation of the transmission, the gear wheel tooth was broken, which made it impossible to continue running this device. The investigation of the damaged area was focused on determining the chemical composition of the inclusions which are present of gear wheel material as well as detecting changes of material contrast in microlocalities close to the defective areas. The method of energy-dispersive spectroscopy and scnanning electron microscopy were chosen for this type of analysis. Furthermore, the micropurity and microstructure of the material were evaluated by methods of optical microscopy and scanning electron microscopy. Using a thermo-emission scanning electron microscope, the microcrack area was evaluated in the mode of secondary electrons and also in the mode of backscattered electrons. In this way, the fracture surface was examined in terms of its micromorphology as well as material contrast.