OBJECTIVE To evaluate the effects of different doses of phytoestrogen (genitein) combined with calcium and vitamin D3 on preventing osteoporosis in ovariectomized (OVX) mice. METHODS 63 female CD-1 mice, 29g average weight, were randomly divided into 7 groups. Including Sham group, OVX group and groups of treatment with calcium, vitamin D3 and genistein in high dose (GH, 67 mg/kg), genistein in moderate does (GM, 33.5 mg/kg), genistein in low dose(GL,16.75 mg/kg), pure genistein (G) and pure 17-betaestradiol (E2). After six weeks treatment, bone mineral density (BMD), bone mineral content (BMC), Biomechanical characteristics bone strength and bone biochemical markers were measured in all mice. RESULTS In the groups of GH, GM and GL, it was stimulative effect of genistein on elevating uterine weight in ovariectomized mice and the effect in GL group is lower. BMD, BMC, length and width of femora were significantly increased in GM group mice than those in OVX mice (P < 0.01), as well as BMD of femora in GL group mice were markedly increased (P < 0.01). Peak load and resilience of femora were the most conspicuously increased in GL group mice than those in others treatment group mice (P < 0.01). In GL group, bone alkaline phosphatase (BALP) increased and tartrate-resistant acid phosphatase (TRAP) decreased (P < 0.01). CONCLUSIONS It was lower stimulative effect of low dose of phytoestrogen (genitein) combined with calcium and vitamin D3 on elevating uterine weight in ovariectomized mice. Low dose of Phytoestrogen (genistein) combined with calcium and vitamin D3 might increase BMD, improve the mechanical strength of bone, promote bone fromation and inhibit bone resorption significantly. It might reduce the dose of genistein administrated and be safter than E2.