Abstract: This paper deals with the lateral vibration characteristics of the diskshaped bevel gear including the lateral vibration modes and stress distribution, vibration excitng force at normal meshing and the conditions under which the lateral resonance occurs. The investigation shows that as vibration modes of this kind of gear are nodal diameters, the tangential tensile stress at the slot bottom of teeth will be maximum, especially at the small end of the bevel gear. Therefore, it is easy to initiate fatigue cracks there.A new theory about the conditions of lateral resonance for the disk-shaped bevel gear is presented and the experimental data are in excellent agreement with the theoretical analysis.