Aim To investigate the effect of catalpol from Radix rehmanniae on the proliferation,differentiation and matrix mineralization of MC3T3-E1 cells in vitro.Methods Catalpol from Radix rehmanniae of different concentration preparations were extracted with ethanol(catalpol ethanol-extract),respectively.A mouse osteoblast cell line MC3T3-E1 was used to determine the potency of catalpol.MTT were applied to determine proliferation of the cell treated by catalpol at different concentrations.Differentiating effects of the catalpol with different concentrations in the cell were evaluated through the examinations of alkaline phosphatase(ALP)activities and bone gla protein(BGP)levels.Von kossa staining method was used to demonstrate the effects of the catalpol on calcification of the cells.Results Catalpol at concentration from 1×10~(-7) to 1×10~(-9) mol·L~(-1) for 24 hours and 48 hours effective promoted the proliferation of osteoblasts of MC3T3-E1 cells line.Catalpol at concentration from 1×10~(-5) to 1×10~(-6) mol·L~(-1) for 48 hours and 72 hours effective stimulated the activity of ALP of osteoblasts of MC3T3-E1 cells line.Catalpol at concentration from 1×10~(-5) to 1×10~(-6) mol·L~(-1) for 8 days and 12 days effective increased the synthesis and secretion of bone gla protein(BGP) of osteoblasts of MC3T3-E1 cells line.Catalpol at concentration from 1×10~(-5) to 1×10~(-6) mol·L~(-1) for 19 days effective increased the mineralized bone nodular structure number of osteoblasts of MC3T3-E1 cells line.Conclusion Catalpol could promote proliferation and differentiation of MC3T3-E1 cells in vitro.Catalpol may be one of effective monomer of Radix rehmanniae on treatment of osteoporosis.