The purpose of this study was to investigate the effects of irradiation on the rat submandibular gland which composed of the epithelial growth factors. The experimental animals were the Sprague Dawley strain rats, which were the rats as the non-irradiated control group and the rats as the experimental group which were divided into groups as the experimental duration of 1 hour, 3 hours, 6 hours, 12 hours, 1 day, 3 days, 1 week, 2 weeks, 4 weeks. The experimental animals were singly irradiated at a dose of 8 Gray gamma ray to their head and neck region by the Co-60 teletherapy unit and sacrificed after each experimental duration. The specimens were stained with H-E and Azan stain and examined light microscopically. The results of this study were obtained as follows. 1. The all of mucous and serous acini in submandibular gland showed similar pattern of changes in structure according to the lapse of time. 2. The acinic cells started to change after 1 hour, and repaired after 12hours with mitosis and proliferation of the cells between acini. The changes were marked after 1day, and repaired gradually in course of time. 3. The duct were dilatated irregularly, and the outline of the eosinophilic stained ductal cells changed indistinctly