To discuse the changes of apoptosis level in small bowl and colon of mice after γ-ray irradiation. The mice were irradiated with different doses (1, 6, 12Gy). The incidence of apoptosis in small bowl and colon were observed at diffifent time (6, 12, 24h)after irradiation using morphological method. The results indicate that there were apoptosis in small bowle of normal mice, the number of apoptotic cell was 0.038±0.059 per whole crypt. No apoptosis was observed in colon of normal mice and irradiated mice; The incidence of apopotosis significantly increased in small bowl after different doses of irradiation ,(p,<,0.05). The apoptosis peak appeared at 12, 24, 6h after 1, 6, 12Gy irradiation; The incidence of apoptosis was higher in small bowl than that of colon after different doses of irradiation and at different time after irradiation. From the results we propose that the radiation-damaged cells might be more effectively removed in small bowle than in colon after irradiation. Radiation-damaged cells may tend to remain in colon and related to later tumorigenesis.