In order to study the crystalline morphology and crystallization mechanism of PET annealed at low temperature, the amorphous PET film, quenched from the melt, was annealed at 90∼120$^{circ}C$ with and without tension for various times. The properties of annealed PET film were measured by density gradient tube, polarizing microscope, infrared spectrometer, X-ray diffractometer and thermal analyzer. The following results were obtained; 1. The crystalline morphology of annealed PET at low temperature was not fringed micellar or bundle-like but spherulitic. 2. Crystallites became more perfect with the increase of annealing time. 3. The rate of crystallization was rapid and the dimensions of crystal growth became larger with the increase of annealing temperature. 4. Local crystallization via chain folding proceeded at low temperature.