This paper investigated fatigue strength of flexible bellows made from austenitic stainless steel, SUS316L. First, tensile and fatigue experiments were performed under load control on the base materials for formed and welded stainless bellows, i.e. SUS316L as well as SUS304, with the sheet thickness between 0.15 and 0.2 mm. The materials exhibited extensive strain hardening which influenced on the fatigue strength. It was demonstrated that the fatigue limits of prestrained materials were higher than those of virgin materials. Since the fatigue limits were higher than the 0.2% proof stresses for the base materials, the strain hardening played an important role on the fatigue behavior. Second, model specimens were cut from the formed and welded bellows and Vickers hardness was measured on the specimen section in order to predict the extent of strain hardening. Fatigue experiments were performed under displacement control. Constant amplitudes of cyclic displacement were applied for the specimens and crack initiations were detected by monitoring the maximum and minimum loads. Finite element method (FEM) was employed to correlate the fatigue strength of the model specimens with that of base materials.