Pueraria mirifica (PM) is a Thai herb which contains high amount of phytoestrogens. It was reported to prevent bone loss in gonadectomized rats. Thus, this study aimed to investigate the therapeutic effects of PM on bone loss in ovariectomized rats. Six months old female rats were divided into 2 groups; sham operation (SH group, n=13) and ovariectomy (OVX group, n=45). After operation, they were kept for 90 days to induce bone loss. Blood samples were collected every 30 days for serum alkaline phosphatase (ALP) and tartrate resistant acid phosphatase 5b (TRAP 5b) assays. On day 90, 5 rats in each group (OVX90 and SH90 groups) were randomly selected and euthanized. Bone was collected and measured for bone mineral density (BMD), bone mineral content (BMC) and %trabecular bone area (%BA). The remaining SH rats (n=8) were gavaged daily with distilled water for 90 days. The remaining OVX rats were subdivided into 5 groups (n=8/group) and gavaged daily with 0, 10, 100 and 1,000 mg/ kg BW/ day of PM (PM0, PM10, PM100 and PM1000 groups, respectively) and 0.1 mg/ kg BW/ day of 17-α ethinylestradiol (EE group) for 90 days. Blood samples were collected every 30 days for serum ALP and TRAP 5b assays. After 90 days of treatment, rats were euthanized and collected bone for BMD, BMC and %BA determinations. The results showed that BMD, BMC and %BA were significantly lower in the OVX90 rats than the SH90 rats (p<0.01), serum ALP levels were higher (p<0.05) throughout the 90 days of bone loss induction period, while the serum TRAP 5b levels was significantly higher only on D30 (p<0.05). After 90 days of the PM or EE treatment, BMD, BMC and %BA of rats were significantly higher than those of the PM0 group (p<0.05). Although serum ALP levels of PM or EE treated groups were not different from those of the PM 0 group, serum TRAP 5b levels were significantly lower (p<0.01), but not depended on doses. Treatment of EE had no effects on serum ALP and TRAP 5b levels, compared to the PM0 group. These results indicate that PM consumption tends to restore the established osteoporosis in OVX rats by reducing bone loss. However, the mechanism of the effects of PM is different from those of synthetic estrogens.