Friction coefficient, relative slip amplitude (fretting amplitude) and dissipation energy per one fretting cycle for steel ball-PMMA (polymethylmethacrylate) in fretting situation are investigated under various levels of normal load and amplitude of steel ball. Friction coefficient increases and relative slip amplitude decreases with fretting cycles in this study. Especially, dissipation energy per one fretting cycle was calculated by inputting a friction force and a relative displacement to a microcomputer. Equations between a tangential force and a tangential displacement based on the theory of elasticity were made by using the results of Mindlin who analyzed the contact of two elastic balls. It was shown that the experimental results of dissipation energy can be explained by these equations.