It was aimed in this study to investigate the fundamental fatigue damage of CVD diamond films deposited on silicon substrate. In order to eliminate complicated dynamic surface interaction, fatigue experiment was performed with a quasi static cyclic load applied by spherical indenters at 10 Hz. The initial fatigue damage appeared on the substrate surface under the diamond film as small cracks, followed by partial debonding of the diamond film. This also meant that silicon was susceptible to fatigue even under the environment hermetically sealed with surface coating. Fatigue lifetime before debonding was successfully characterized as stress–number of cycles (S–N) diagram.