The present study aimed at investigating the effects of Puerarin(PR), a major isoflavonoid isolated from the Chinese medicinal herb Puerariae radix, on bone metabolism and the underlying mechanism of action. The in vivo assay, female mice were ovariectomized(OVX), and the OVX mice were fed with a diet containing low, middle, and high doses of PR(2, 4, and 8 mg·d~(-1), respectively) or 17β-estradiol(E_2, 0.03 μg·d~(-1)) for 4 weeks. In OVX mice, the uterine weight declined, and intake of PR at any dose did not affect uterine weight, compared with the control. The total femoral bone mineral density(BMD) was significantly reduced by OVX, which was reversed by intake of the diet with PR at any dose, especially at the low dose. In the in vitro assay, RAW264.7 cells were used for studying the direct effect of PR on the formation of osteoclasts. PR reduced the formation of tartrate resistant acid phosphatase(TRAP)-positive multi-nucleated cells in the RAW 264.7 cells induced by receptor activator for nuclear factor-κB Ligand(RANKL). MC3T3-E1 cells were used for studying the effects of PR on the expression of osteoprotegerin(OPG) and RANKL m RNA expression in osteoblasts. The expression of OPG m RNA and RANKL m RNA was detected by RT-PCR on Days of 5, 7, 10, and 12 after PR exposure. PR time-dependently enhanced the expression of OPG m RNA and reduced the expression of RANKL m RNA in MC3T3-E1 cells. In conclusion, our results suggest that PR can effectively prevent bone loss in OVX mice without any hyperplastic effect on the uterus, and the antiosteoporosis activity of PR may be related to its effects on the formation of osteoclasts and the expression of RANKL OPG in osteoblasts. The present study aimed at investigating the effects of Puerarin (PR), a major isoflavonoid isolated from the Chinese medicinal herb Puerariae radix, on bone metabolism and the underlying mechanism of action. The in vivo assay, female mice were ovariectomized (OVX), and the OVX mice were fed with a diet containing low, middle and high doses of PR (2, 4, and 8 mg · d -1, respectively) or 17β-estradiol (E 2, 0.03 μg · d -1) 1)) for 4 weeks. The total femoral bone mineral density (BMD) was significantly reduced by OVX, which The reduced intake of the diet with PR at any dose, especially at the low dose. In the in vitro assay, RAW 264.7 cells were used for studying the direct effect of PR on the formation of osteoclasts. PR reduced the formation of tartrate resistant acid phosphatase (TRAP) -positive multi-nucleated cells in the RAW 264.7 cells induced by receptor a ctivator for nuclear factor-κB Ligand (RANKL). MC3T3-E1 cells were used for studying the effects of PR on the expression of osteoprotegerin (OPG) and RANKL m RNA expression in osteoblasts. The expression of OPG m RNA and RANKL m RNA was detected by RT-PCR on Days of 5, 7, 10, and 12 after PR exposure. PR time-dependently enhanced the expression of OPG m RNA and reduced the expression of RANKL m RNA in MC3T3-E1 cells. suggest that PR can only prevent bone loss in OVX mice without any hyperplastic effect on the uterus, and the antiosoporosis activity of PR may be related to its effects on the formation of osteoclasts and the expression of RANKL OPG in osteoblasts.