Torsional fretting tests of UHMWPE against titanium alloy ball (TC4) had been carried out. A frictional torque-angular displacement (T-theta) curve was used to analyze the kinetics behaviors of torsional fretting mode. The wear morphology and damage mechanisms of UHMWPE were studied based on examinations by scanning electron microscopy (SEM). It is found that the contact stiffness and friction-dissipated energy initially rise and then gradually reach a steady state. The worn surface is characterized by adhesion in the centre zone, while in the outer annulus, ripples, ploughs and delamination appeared. In addition, a transfer film is found on the surface of titanium alloy ball. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.