Abstract: Objective 　Therapy effection and mechanism of S180 tumor cell by ¹²⁵Ⅰ seed implantation. Methods 　The study use S180 tumor cell, 36 male Kunming mice were divided into 3 groups in random, 12 mice each group :cont rast, radiation and ¹²⁵Ⅰseed implantation. Radiation :4-MV X-ray, 200 cGy/ fraction, three f raction. ¹²⁵Ⅰ seed implantation :insert the seed into the mouse tumor using the special-made needle. One seed was implanted into six mice, two into another six mice. The model mice of radiation were sacrificed at 6h, 30h and 54h. The model mice of seed implantation were sacrificed at 4 d and 8 d. The fresh tumor tissure sample were examined apoptosis by TuNEL, measured the apoptois index ( AI) and p53 were measured by immunocytochemistry. Results 　(1) The cont rast group can also have spontaneous apoptosis without t reament . But the apoptosis appeared late with lower apoptosis index. (2) Radiation can induce cell apoptosis and the apoptosis index increased with the time went by. (3) ¹²⁵ Ⅰseed implantation can induce S180 cell apoptosis. The peak value within 4 d and with the increase of implanted seed, the AI increased. The comparsion between 2 seeds and 1 seed has significant difference within 4 d and 8 d ( P < 0. 05) . (4) p53 count not be found in S180 tumor cell. Conclusion 　(1) S180 tumor cell are less sensitive to radiation. The radiosensitivity is not realated to mutated-type p53 (mtp53) . (2) ¹²⁵Ⅰ seed implantation and radiation all can induce S180 tumor cel apoptosis. The induced apoptosis mechanism is not related to mutated-type p53. (3) ¹²⁵Ⅰ seed implantation is effective method in the t reament of carcinomas.