Fretting damaged surfaces of PMMA (polymethyl methacrylate) and steel balls in contact are directly and microscopically observed by optical microscope for various level of normal load, amplitudes of steel balls and fretting frequencies. It is found that corrugation occurs on the surface of PMMA during fretting and it is closely related with the wear of steel balls. After the initiation of corrugation, two types of wear are observed in our experiments : (a) the steel ball continues to slide on PMMA and the wear debris of the steel ball is enveloped in the softened PMMA ; and (b) the steel ball adheres to the corrugation and the wear debris accumulates at the boundary of adhered area. To study the cause of corrugation, the distribution of temperature of the fretting surface is numerically analyzed by the nonlinear transient heat conduction equation with the heat generated by the dissipation of energy during fretting. As a result, the increase of temperature by the dissipation of energy is very little, and it may be attributed to the viscoelastic property of PMMA.