Hydrogen uptake, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel with a newly developed coating (alumina/aluminum/Fe–Al) were presented. The developed coating had an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270 °C. Measurements of bulk and local hydrogen by thermal desorption analysis and secondary-ion mass spectrometry (SIMS) suggested that the excellent resistance was attributed to the reduction in permeation areas by interfacial hydrogen trapping between the aluminum and Fe–Al layers. Tensile tests of a smooth, round-bar specimen, and fatigue tests of a circumferentially notched specimen after exposure to 100-MPa hydrogen gas at 270 °C were performed in air at room temperature (RT). These properties of the coated specimens were not degraded by hydrogen exposure, whereas those of the noncoated specimens were significantly degraded. Hydrogen-pressure cycle tests of coated, tubular specimens with an inner notch in 95-MPa hydrogen gas at 85 °C also demonstrated that the fatigue life was improved by the coating.