Fretting fatigue mechanism of rapidly solidified powder aluminum alloy has been studied by model tests and analysis using fracture mechanics. The factors which influences upon fretting scar formation and fatigue crack propagation were the main concerns in the present work. In order to investigate the mechanism of fretting scar formation in detail, fretting wear tests in which small amplitude oscillatory movement occurred in the contact region were carried out. Test results showed that the size of fretting scar increased with increasing tangential force coefficient. Characteristics of fretting fatigue crack propagation were analyzed using fracture mechanics. The fatigue limits under fretting conditions were estimated by connecting the applied stress intensity factor range calculated from applied cyclic stress and tangential force, with the threshold stress intensity factor range of small crack. The predicted fatigue limits were in good agreement with the experimental results of fretting fatigue tests.It is concluded from these test results and analysis that fatigue strength under fretting conditions is correlated with both tangential force coefficient and tangential force. That is to say, fretting scar formation is controlled by tangential force coefficient and crack propagation characteristics are controlled by tangential force. Based on the fretting fatigue mechanism mentioned above, a method to design is presented.