This study examined the estrogenic activity produced by aqueous extracts of silkworm (Bombyx mori) pupae in ovariectomized (OVX) rats. The components of silkworm pupae were extracted in distilled water at room temperature for 6 hours. The ovaries of six-week old female rats were then bilaterally removed. One week after OVX, the animals were treated with 200, 400 or 600 mg/kg/day of silkworm pupae extracts. The body weights of the OVX rats increased remarkably compared to the control rats, however their relative uterus weights to body weights decreased significantly. Treatment with the aqueous extracts of silkworm pupae dramatically improved the decreased uterus weights of OVX rats, with the highest increase observed in treatment with 200 mg/kg/day of the aqueous extracts. Additionally, treatment with aqueous extracts (200 mg/kg/day) of silkworm pupae significantly elevated the serum 17beta-estradiol contents of OVX rats when compared to the control animals. To examine the toxic effects of silkworm pupae on the hepatic functions of OVX rats, the levels of serum glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) were measured. The serum GOT and GPT levels did not change in response to the administration of aqueous extracts (200, 400 and 600 mg/kg/day) for 4-weeks. Taken together, these results suggest that the aqueous extracts of silkworm pupae may have estrogenic activity, which suggests that silkworm pupae may be useful in the prevention and/or treatment of menopausal disorders caused by deficiencies in female sexual hormones, including estrogen.