In order to solve the global warming problem, development and commercialisation of fuel cell (FC) systems are being promoted. In the FC systems, many stainless steels are used for the components such as the liners of ultra-high pressure vessels, piping, bearings, and springs. Such components are directly exposed to hydrogen environments under cyclic loading. It has been reported that hydrogen degrades the mechanical properties, especially ductility of metallic materials [
]. Moreover, the degradation of fatigue strength of metallic materials due to hydrogen intrusion is a matter of concern from a practical point of view. In our previous investigations [
], hydrogen was artificially (electro-chemically) charged into the specimens of several candidate materials, and it was revealed that hydrogen affects the slip band morphology and fatigue crack growth behaviour. In this study, hydrogen intrusion and fatigue crack growth behaviour in stainless steels exposed to high pressure hydrogen environments were investigated at room temperature and in laboratory air to clarify the effect of the intruded hydrogen on the fatigue crack growth.