Objective To study the mechanism of inhibiting mammary cancer bone metastasis of the warming kidney medicines Shechuangzi（Fructus Cnidii）-Buguzhi（Fructus Psoraleae） from the OPG/RANKL/RANK system of regulating osteoclast differentiation.Methods The 42 successfully made nude mice models with mammary cancer bone metastasis were randomized into model group

zoledronic acid group

Cnidium group

Psoralea group

2:2 ratio group

1:3 ratio group

and 3:1 ratio group

with 6 in each.The other 6 normal nude mice were taken as a normal group.They were given the corresponding liquid medicine by gavage respectively

but the zoledronic acid group was given intraperitoneal injection

and the normal group was given normal saline by gavage

for 6 weeks.The changes of body weight

pathological manifestations of bone metastases focus

and expression of osteoprotegerin and receptor activator of nuclear factor-kappa B ligand mRNA of nude mice were observed.Results The weight loss rate of the 3:1 group and 2:2 groups were significantly lower than other compatible groups

and that of the 2:2 group was lower than of the 3:1 group.The amount of bone TRACP（+） cells of different compatible groups was all statistically different

and the 2:2 group was superior to other compatible groups.The different compatibility of Shechuangzi（Fructus Cnidii） and Buguzhi（Fructus Psoraleae） could up-regulate the OPG expression to different degrees and down-regulate the RANKL expression

thus it was regulating the OPG/RANKL secretion ratio from the gene level.The effect of 2:2 group was better than other compatible groups in result.Conclusion All different compatibilities of Shechuangzi（Fructus Cnidii） and Buguzhi（Fructus Psoraleae） have inhibition effect on mammary cancer bone metastasis

while the effect of 2:2 group is the most superior.Its possible mechanism is probably related with the regulation of OPG/RANKL secretion ratio.