The inhibitory effects of a Japanese herbal medicine, Chujo-to, on the progress of bone loss induced by ovariectomy in rats were investigated. Ovariectomized rats were administered with Chujo-to during weeks 7-14 after ovariectomy. At 14 weeks, the bone mineral density of the tibia from ovariectomized (OVX) rats had decreased by 27% compared with those in the sham-operated rats, and by a 18%-21% and 16% decrease after the administration of Chujo-to and 17 beta-oestradiol, respectively. The surface of a trabecular bone of the tibia in ovariectomized rats had a porous and fibrous appearance, while that of the same bone in sham-operated rats was composed of fine particles VSports手机版. After the administration of Chujo-to or 17 beta-oestradiol, the surface of trabecular bone maintained the porous and fibrous appearance. The uterine weight was not restored by Chujo-to but by 17 beta-oestradiol. These results suggest that Chujo-to has an efficacy on the osteoporosis of rats similar to 17 beta-oestradiol, but with a different mechanism. .