Abstract: Objective: To reveal the biological effect and valid dosage of high single-dose irradiation in animal experi -ment. Methods:We inoculated subcutaneouly human pancreatic carcinoma cell line (MIA PaCa-2) in lateral of right lower extremity of athymic mouse to raise transplantation tumor. While the median diameter of transplantation tumor reached 10mm approximately,animals were randomly divided into7 groups ( 6 animals per group) and fixed under conscious condi-tion to receive radiation treatment of different dosage in one fraction( 0、2、5、10、17、25、35Gy). All mice were kept on breed-ing and observed the volumes of gross tumors, then calculated the growth time of transplantation tumors and draw the growth retardation curves. Results: During the whole process of experiment, the weigh changes in each group showed the same trendency. With increasing dosage per fraction, cutaneous reaction on the surface of animal neoplasma was mainly moist yellow effusion and became more and more severe.When exposure dose is less than 10Gy, all animals showed simi-larly the effect of tumor growth retardation was not obvious seen. When transplantation tumors exposured under more than 10Gy irradiation in one fraction , good biological effect of tumor growth retardation was obviously observed, which was pos-itively correlated to the exposure dosage. The severity of tumor growth retardation in two different treated groups was statis -tically different( P<0.05).Growth retardation time of transplanted tumors (tumor volume decrease first and then re-increase to original volume) in 10, 17, 25and 35Gy group was respectively 3 weeks,6 weeks, or more. Tumor growth curve and tu-mor volume inhibition rate of transplantation tumors in athymic mouses after exposuring to different irradation dose in one fraction reflected tumor volume change more directly. The effect of tumor growth retardation was obviously direct related to irradiation dosage. Conclusion : The radiation therapy method of high single-dose (more than10Gy in one fraction) in trans -planted tumors appeared good biological effect. And additionly the effect of tumor growth retardation was obviously directly related to the irradation dosage. Above all, from the good biological effect result of the experiment, it seems the method of high single-dose irradiation can be a better clinical radiotherapy method.