AISI 420 martensite stainless steel was plasma nitrided with/without shot peening (SP) previously at 350 °C. The FF resistance of researched material was evaluated using a rotating bending fatigue machine and a home-made apparatus. The results indicated that low-temperature nitriding alone and the combined treatment both improved the FF resistance of AISI 420 stainless steel significantly. However, the later did not lead to higher FF resistance than the former. FF cracks tended to initiate at microcrack defects induced by SP.