Nonisothermal crystallization rate of PET was derived by using the data obtained from the DSC. The profile changes of temperature and crystallinity in the mold with the injection temperature, mold temperature and specimen thickness were calculated through the computer simulation. To verify the propriety of this computer simulation, the calculated values were compared with the data of crystallinity measured experimentally with the injection molded specimen. For neat PET, the profiles of temperature and crystallinity within the specimen were relatively uniform, but cooling time more than 5 min was required due to slow crystallization rate. On the other hand, for the nucleated PET, the crystallization was completed in 3 min, but considerable change in the temperature and crystallinity with the position of specimen was observed. As the mold temperature or specimen thickness was increased, the crystallization at the center position of mold was delayed due to the decreased cooling effect. Especially, the effect of specimen thickness on crystallization was found to be more significant. The variation in morphology with injection molding condition had an effect on the mechanical property of specimen. The injection molded specimen at higher temperature showed lower impact strength because of the relatively larger spherulites.