Recently, spiral bevel gears have come to be used widely as transmission gears of motor cars. However, there have been very few studies hitherto which deal with spiral bevel gears, and many problems still remain to be solved. Under the present day situations, the dynamic behavior of the Gleason-type and the Oerlikno-type spiral bevel gears was chosen as a subject of this study. That is to say, stresses at the tooth root under various running conditions were examined. From these experimental results, difference in characteritics of Gleason-type and Oerlikon-type spiral bevel gears could be clarified.