Surface carboxyl groups were formed during the Co-60 gamma-ray irradiation of poly(tetrafluoroethylene) (PTFE) in air. Fourier transform infrared spectroscopy enables the detection of surface carboxyl groups. The contact angles were used to calculate the dispersive and polar components of the surface free energy according to a two-liquid method. The gamma-ray irradiation of PTFE mainly caused degradation of the polymer. The concentration of carboxyl groups, the wettability, the friction, and the dispersive and polar components of the surface energy and the crystallinity on PTFE surface were increased, while the particle size of PTFE decreased with increasing irradiation dose. A highly modified PTFE was used to reduce the aqueous liquid repellent properties of PTFE. A 20 kGy dose for modified PTFE surface was suitable in air additivity in antifriction, anticorrosion, antifouling, lubrication, and noise reduction coatings.