Fatigue and fretting tests were carried out with 15 Cr 11 MoV steam turbine blade steel in air and vapor environments. The steel was in the as-heat-treated and as-shot-peened conditions. Both testing ambience and shot peened residual stress could effect the fretting fatigue strength of the steel. The AES and Mossbauer spectrometry experiments indicated that the oxide layer in the fretted scar and the debris had different structures, depending on whether they were formed in air or vapor. This resulted in a change in the tribological properties between the contact surfaces and in the fretting fatigue strength of the steel. However, the environmental effects became less important in compressive stresses.