The dynamic level of immunosuppressants such as alpha-fetoprotein(α-FP), gestation associated protein, progesterone, estradiol, chorionic gonadotropin, etc. of peripheral sera and the regulatory mechanism of cellular immunity in the peripartum stages in sows were determined by advanced radioimmunoassay (RIA) and immunochemistry methods in this study. The effects on lymphocyte cultivated in vitro by the immunosuppressants mentioned above were tested by cell culture technology, respectively. The results were as follows: (1) α-FP: The level of α-FP of peripheral sera in the stage of ante-parturition was slightly higher than that of post-parturition in sows, but it didn't show statistical difference. The concentration of α-FP of peripheral sera in conceptus sows had no obvious effect on lymphocyte cultivated in vitro, and it indicated that α-FP was not the major immunosuppressant in the pregnancy of sows. However, the α-FP, whose concentration was equal to that of amniotic fluid, had obvious inhibition on lymphocyte cultivated in vitro. (2) Gestation associated protein: The level of gestation associated protein was maintained highly (100-162 mg/L) in peripheral sera and amniotic fluid in the stage of ante-parturition in sows, then descended gradually after parturition and disappeared step by step 5-10 d after parturition. The gestation associated protein, whose concentration were equal to that of peripheral sera and amniotic fluid, were added to lymphocyte culture in vitro, and the effect on lymphocyte activity was not observed yet. This showed that gestation associated protein was not the major immunosuppressant in the peripartum stage in sows. (3) Estradiol and progesterone: Estradiol or progesterone at the level of sera in pregnant sows, could lower the rate of lymphocyte transformation and the level of cellular immunity. (4) Chorionic gonadotropin: The level of chorionic gonadotropin of peripheral sera in the stage of ante-parturition was slightly higher than that of post-parturition in sows, but it didn't have statistical difference. The chorionic gonadotropin, whose concentration was equal to that of sera, was not yet observed obvious effect on lymphocyte cultivated in vitro. (5) Added the five above-mentioned immunosuppressants to lymphocyte culture in vitro, whose concentration were equal to those of sera in pregnant sows, they could drop the rate of lymphocyte resette formation and lymphocyte transformation, lower the level of cellular immunity and reduce the concentration of IL-2 which synthesized and secreted by lymphocyte in culture remarkably. Their inhibitory intensity of cellular immunity was evidently higher than that of any single immunosuppressant.