Abstract: Theγ-ray radiation was used to modify the surface activity of pitch carbon fiber to improve the interfacialadhesion between the fiber and mat rix. The surface st ructures of the unt reated and t reated pitch carbon fibers wereinvestigated by AFM and XPS , and the measurement s of contact angles were used to understand the change of thesurface energy of the pitch carbon fibers. The effect s of γ-ray radiation on mechanical properties of the carbon/ carbon composites were investigated. The result s show thatγ-ray radiation increases the carbonyl functional group andthe surface roughness , improves the impregnation of the carbon fibers , decreases the composites porosity , andenhances the mechanical properties of composites.