In this paper, three commercial polymers (polytetrafluoroethylene [PTFE], polyetheretherketone [PEEK], and polyimide [PI]) were irradiated by gamma rays in the ambient air. The changes in microstructure, mechanical, and tribological properties of these three polymers after irradiation were investigated comparatively. The results display that both the surface and internal structures of PTFE are degraded due to the irradiation chemical reaction, and the molecular chain scission at the surface is more severe than that at its internal as a result of the involvement of oxygen. The oxidative degradation also plays a dominant role in the PEEK surface, but the molecular chain crosslink is dominant in the PEEK internal. The top layer of PI also shows the characteristics of oxidative irradiation degradation, but its internal exhibits excellent irradiation resistance and no structure change occurs even at irradiation doses up to 20 MGy. The microhardness and scratch resistance of irradiated surfaces for all three polymers decrease but only the scratching damage mode of PTFE changes after irradiation. Friction experiments show that the friction coefficients of PTFE increase but that of PEEK decrease after irradiation. The wear rates on the irradiated surfaces of all three polymers increase compared with the unirradiated samples. Moreover, there is a depth gradient effect on the wear properties of both irradiated PTFE and PEEK polymers. The changes in wear rates of irradiated surfaces are consistent with the structural variations of all three polymers.