Keishibukuryogan is a traditional Japanese medicine widely administered to patients with menopausal symptoms. Because humans use it on a long-term basis, we believed that a carcinogenicity study was warranted. We orally administered keishibukuryogan (TJ-25) extract powder to 6-week-old Sprague-Dawley rats [Crl:CD(SD)], which were divided into four dosage groups-0 (water for injection), 100, 500 and 2,500 mg/kg/day for 24 months. We found that TJ-25 did not affect the survival rate of either sex. Furthermore, it did not affect the clinical condition of the rats, number of superficial tumors found by palpation, body weight, food consumption, hematology, or gross pathological findings. The severity of degeneration of muscle fiber in the femoral skeletal muscle increased slightly in males and females in the 2,500 mg/kg/day group, but TJ-25 did not increase the number of tumors found on histopathological examination. In our study, oral administration of TJ-25 extract powder in rats for 24 months was not associated with an increased incidence of tumors.