Abstract:After 30 days' subcutaneous injection of different doses of thymosin into the female mice of different ages (1 month, 3 months), serum hormone levels of Follicle-Stimulating Hormone (FSH), Estradiol-2 (E2), Thyroid-Stimulating Hormone (TSH) and Insulin (INS) were detected to determine the effects of thymosin. The results show that for 1 month mice with different doses of thymosin, FSH and E2 levels are decreased significantly or very significantly(P<0.05, P<0.01), TSH levels are increased significantly or very significantly(P<0.05, P<0.01), INS levels are decreased, and high dose thymosin makes a significant difference in INS(P<0.05). For 3 month mice with different doses of thymosin, FSH levels are decreased and high dose thymosin makes a very significant difference in FSH(P<0.01), TSH levels are increased and high dose thymosin makes a significant difference in TSH(P<0.05). E2 and INS levels are decreased with no significant difference. It is concluded that thymosion influences female mice's serum hormone level, which in turn affects its endocrine system.