Abstract: The tangential fretting experiments with a Ti6Al4V ball on a CoCrMo plat contact were carried out in different media. Microscopic analysis was used to reveal the fretting running characteristics and damage mechanisms. The results show that tangential fretting mainly run in partial slip regime and mixed regime. With the increase of amplitudes, F_t-D curves transformed from linear into elliptic form. At the end of fretting and large amplitude, F_t-D curves of mixed regime presented parallelogram. In partial regime, the friction coefficient was low and stable, and the mild wear was observed. However, in the mixed regime, two viriation modes of friction coefficient were attributed to the variation of amplitudes. In the smaller amplitude mixed regime, debris accumulation at the edge of the wear scar was observed, and adhesion occurred in the center of wear scar. While in the larger amplitude mixed regime, abrasive wear was the main wear mechanism.