The properties of molecular motion and trap of γirradiated poly¬(ethylene terephthalate) (PET) are studied by the method of TSC. ,60,Co γ-irradiation of a larger dose (500—5000 kGy) leads to the breaking of macromolecular chain and the increase of group dhensity of phenzyl with oxygen in PET. The α-peak of shortcircuit thermally stimulated current (corresponding to the glass transition temperature)shifts to lower temperature when irradiation dose increases. The mean depth of trap level, the initial density of charge carriers and maximum of ρ-peak current increase with the rise of irradiation dose. But γirradiation has not remarkable effect on the activation energy and the time constant of dipolar thermal relaxation for the main chain segmental motion in amorphous region of ,γ, irradiated PET electrets.