@@The purpose of this study was to determine the time-dose-effect of total body X-ray irradiation on lymphocytes in lymph node and peripheral blood in Tibet minpigs. Forty-eight Tibet minpigs were assigned into 6 groups including 5 experimental groups with 9and the control group with 3. The minipigs in experimental groups were subjected to a total body X-ray irradiation of 2, 5, 8, 11, and 14 Gy respectively. Lymph nodes and peripheral blood samples were collected at 6, 24 and 72 hours after X-ray exposure and received histological microscopy examination and apoptosis analysis. Histology observation showed that the number of lymphocytes decreased within the lymph nodes with the increase of radiation doses and exposure time.The observation of transmission electron microscopy (TEM) showed that below 11 Gy were typical apoptotic cells while at 14Gy was dominantly necrotic cells.The apoptotic rate of lymphocytes in the lymph nodes was positively correlated with radiation dose in the range of 2-11 G-y, and reached the maximal level (39.4±2.8) at 24h after 11Gy irradiation,followed by a decrease in the apoptotic rate,but still higher than that of control group.The number of lymphocytes in the peripheral blood samples was decreased significantly by increasing of radiation dose and exposure time.We conclude that early damage of lymphocytes by total body X-ray irradiation is a dose and time dependant below 11 Gy and before 24h post irradiation,and that the dosage of irradiation less than 11 Gy induced apoptosis, whereas the dose at 14 Gy resulted in necrosis in lympbocytes of the lymph nodes.