Fatigue tests were performed using circumferentially notched, round-bar specimens with a stress concentration factor, Kt, of 6.6 for Type 304, meta-stable, austenitic stainless steel. The tests were carried out in ambient air and in hydrogen gas at a pressure of 0.7 MPa at room temperature. In the relatively short fatigue-life regime, the specimen showed a marked decrease in fatigue life. In contrast, in the longer-life regime, the specimen showed no degradation in fatigue life in hydrogen gas. The fatigue life curve and fatigue limit were predicted by assuming that the notch was equivalent to a circumferential crack, with the predicted values subsequently compared with the experimental results. With regard to the low-alloy steel, JIS-SCM435, it has been reported that the predictions were in good agreement with the experimental data [1]. However, there is a disparity between what was predicted and the actual experimental results in the case of Type 304. The reasons for this divergence are also discussed in relation to the yielding condition, as well as to the cyclic-plastic deformation behavior at the notch root.