Abstract: Reports the experimental investigation on the reliability of gear-tooth bending fatigue strength for 25Cr2MoV ionitriding gear. The tests were carried out on a Electro-magnetic resonance fatigue test ma-chine of type STRON 1 603. The grouping test method at four constant stress levels was applied for short life-span areas while the stress up-and-down test method were used for long life-span areas. The tested data were then Processed with statistic method. Complete C-R-S-N curves were thus fitted and as a result, the values of limits of bending fatigue under various reliabilitys were gained.