Objective: To explore the mechanism of icariin in inhibiting the osteoclast differentiation via detecting the mRNA expression levels of estrogen receptor α(ERα) and receptor activator of NF-κB (RANK) in osteoclast induced from RAW264.7. Method: RAW264.7 cells were induced into osteoblasts with receptor activator of nuclear factor κB ligand (RANKL) (50 μg·L-1)

and were identified by tartrate resistant acid phosphatase(TRAP) staining and bone resorption pit formation. After RAW264.7 cells were treated with different concentrations (1×10-5

1×10-6

1×10-7 mol·L-1) of icariin for 5 days and 9 days

TRAP staining

and bone resorption pit formation analysis were conducted. After treatment for 6 days

the gene expression levels of(MMP-9)

cathepsin-K (CK)

TRAP

RANK and ERα in osteoclasts were detected by RT-PCR. ICI182780

an estrogen receptor antagonist

was used to invalidate the regulatory effect of icariin on ERα/RANK pathway. Result: Icariin could significantly inhibit the number of osteoclast formation and number of bone resorption pits(P<0.05)

significantly down-regulate the gene expression levels of MMP-9

CK

TRAP and RANK in the osteoclasts(P<0.05)

and up-regulate the gene expression of ERα.ICI182780 could inhibit the icariin in up-regulating the gene expression level of ERα and down-regulating the gene expression level of RANK. Conclusion: Icariin could inhibit osteoclast differentiation and bone absorption function

which may be achieved via increasing ERα mRNA expression and decreasing RANK mRNA expression.