In this study, the structure of PET films, which one is drawn after annealed and the other is annealed after drawn, were investigated. Measurements were carried out with density method for crystallinity and x-ray diffraction method for crystallite size and degree of orientation. By the use of Avrami equation, the rate of crystallization and the type of crystal formation have been studied. In this study, the annealing temperatures are 90, 100, 120, 135$^{circ}C$ and the annealing times are 3, 10, 31, 60, 120, 316, 600, 1200mins. The results obtained are as follows ; The value of crystallinity is larger in the films annealed after drawn than in those of drawn after annealed. And, in the same annealing conditions, the crystallinity of annealed after drawn is smaller than undrawn films. The size of crytsallite is not so much different from each other. The degree of orientation of films annealed after drawn is even higher than that of films drawn after annealed. The Avrami equation was applied to the films annealed without drawn. At these results the rate of crystallization is faster with increasing annealing temperature and the type of crystal formation is thought to be nearly rod-like.