In order to clarify the morphology and the physical properties changes of Polyethylene terephthalate (PET) tire cord in rubber matrix, it was ammonolysed in liquid ammonia and hydrolysed in saturated-steam with various time and temperature, respectively. It was found that the intrinsic viscosity of tire cord decreased with treating time, especially at the early stage of 5 hours. The intrinsic viscosity and the specific stress of PET tire cords were found to depend on the broken bonds of polymer chain, especially the tie molecule. The apparent crystallinity was shown to increase remarkably within 5 hour and then, increase smoothly. We supposed that the Increase of crystallinity was caused by the degradation of amorphous region by ammonolysis and hydrolysis, and the water molecule acting as plasticizer. But the crystallite size was decreased smoothly because of the degradation of crystalline region by ammonolysis and hydrolysis.