Objective: To investigate the effect of icariin on the proliferation, differentiation, and the mRNA expressions of Cbfαl, BMP2, BMP4 of rat osteoblasts. Methods: Primary rat osteoblastic cells were obtained by sequentia collagenase/trypsin enzyme digestion from calvarial bones of new born ( within 24 h) SD rats and were identified by Alkaline phosphatase and alizarin red staining. The passage 3-5cells were treated with icariin at the concentration of 0 mol/L, 10~(-8)mol/L, 10~(-7)mol/L, 10~(-6)mol/L,10~(-5)mol/L, 10~(-4)mol/L for 24 h, 48 h, 72 h, and the proliferation of the cells was measured by CCK-8assay. The proliferation index was detected by Flow Cytometry and the activity of alkaline phosphatase was determined by p-Nitrophenyl phosphate (pNPP) method after being treated with icariin at the concentration mentioned above for 48 h. The total cellular RNA was extracted 48 h after being treated with icariin at the concentration of 10~(-6)mol/L, and the expressions of Cbfα1, BMP2, BMP4 mRNA were examined by real-time PCR. Results: Icariin showed no effect on the proliferation of osteoblasts, but improved ALP activity. The Cbfα1, BMP2, BMP4 mRNA were significantly upregulated after icariin treatment. Conclusion: Icariin could promote the differentiation ability of rat osteoblasts through upregulating the Cbfα1, BMP2, BMP4 mRNA expressions.