In this study, the tribological behavior of ultra-high-molecular-weight polyethylene (UHMWPE) against a GCr 15 steel ball during fretting wear conditions was investigated using an oscillating reciprocating tribometer. The aim of this study was to characterize the critical value of normal load and stroke corresponding to this transition in UHMWPE worn surface at room temperature. Results showed that there existed a critical value of load or stroke at fixed condition. The friction coefficient and wear volume loss of UHMWPE at or near the critical values of load and stroke exhibited extreme changes. Based on observation of the worn surface by scanning electron microscopy (SEM) and 3D surface profiler measurements, it can be found that damage to the worn surface can be linked to the contact load and stroke. In addition, results showed that during the process of fretting wear under different load or stroke conditions, the gross slip regime dominated throughout the whole test period.