Abstract: In order to evaluate the effect of Psoralea corylifolia L. extracts and Psoralen with different concentrations on osteoblasts cultured in vitro. The proliferation and the activity of alkaline phosphatase（ALP）were measured by MTT(tetrazolium salt test) and PNPP(P-nitrophenyl phosphate disodium)， respectively，and the cell-cycle analysis was examined with flow cytometer by PI(propidium iodide) staining. The results indicated that 10 and 10^-3 mg·mL^-1 of Psoralea corylifolia L. extracts could remarkablely promote osteoblasts proliferation. Psoralen at lower concentrations（10^-7，10^-8 mol·L^-1） could promote proliferation of osteoblasts， while it could inhibit proliferation at higher concentrations（10^-4 ，10^-5 mol·L^-1）. ALP activity was significantly increased by different concentrations of Psoralen. The percentage of G1 phase cells was decreased，while the S and the G2 phase were increased. It is suggested that Psoralea corylifolia L. extracts and Psoralen，which promote the proliferation of osteoblasts with a phytoestrogenic effect， can also induce the transformation from the G1 phase to either the S phase or the G2 phase. Psoralen may play an important role in differentiation of osteoblasts.