This study was performed to examine the relationship between the anti-tumor effects of herbal medicine and endometrial carcinoma with ER-related mechanisms. An endometrial cancer cell line (Ishikawa) was used for this study. The cell viability and expression of estrogen receptors (ER) were determined by MTT and RT-PCR. A dose-dependent decrease of viability and apoptosis of the cancer cells was generated by exposure to the herbal medicines, Juzen-taiho-to or Shimotsu-to. The expression of ER-alpha mRNA, but not ER-beta mRNA was suppressed by Juzen-taiho-to or Shimotsu-to in an endometrial cancer cell line. The anti-tumor effect of these herbal medicines against endometrial carcinoma might be correlated to the ER-alpha related mechanism.