Background lcariine is a flavonoid isolated from a traditional Chinese medicine Epimedium pubescens and is the main active compound of it. Recently, Epimedium pubescens was found to have a therapeutic effect on osteoporosis. But the mechanism is unclear. The aim of the study was to research the effect of lcariine on the proliferation and differentiation of human osteoblasts.Methods Human osteoblasts were obtained byinducing human marrow mesenchymal stem cells (hMSCs) directionally and were cultured in the presence of various concentrations of lcariine. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was used to observe the effect of lcariine on cell proliferation. The activity of alkaline phosphatase (ALP) and the amount of calcified nodules were assayed to observe the effect on cell differentiation.The expression of bone morphogenetic protein 2 (BMP-2) mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR).Results Icariine (20 μg/ml) increased significantly the proliferation of human osteoblasts. And, lcariine (10 μg/ml and 20μg/ml) increased the activity of ALP and the amount of calcified nodules of human osteoblasts significantly (P＜0.05).BMP-2 mRNA synthesis was elevated significantly in response to lcariine (20 μg/ml).Conclusions lcariine has a direct stimulatory effect on the proliferation and differentiation of cultured human osteoblastcells in vitro, which may be mediated by increasing production of BMP-2 in osteoblasts.