A resonance type gear fatigue tester has been developed for fast and efficient evaluation of tooth-root fatigue strength. This tester is a sort of pulsating-type, and operates under quasi-resonance condition. One test gear is held stationary, and the mating gear fastened to a vibratory shaft oscillates against the stationary gear. The torsional vibration of the shaft is excited by a rotating eccentric. The torque amplitude is controlled automatically by varying the rotational speed of the eccentric and is maintained during a test. Fatigue tests and measurements of tooth-root strain were conducted on three kinds of helical gears, whose results were compared with those of a running-type fatigue tester. The results indicated that the tooth-root fatigue strengths with the resonance-type tester agreed with the running-type tester by taking the compressive strain which occurred at the tooth-root on the tension side in meshing, the dynamic load and the supporting rigidity in to account.