Objective To observe the effect of mistletoe polysaccharose on proliferation and apoptosis of osteoblast and to explore the possible mechanism. Methods The mistletoe polysaccharose was extracted and made different concentrations (0.625 g/L, 1.25 g/L, 2.5 g/L, 5 g/L) to treat mouse skull bone cell line MC3T3-E1. Cell cycle and apoptosis were detected by flow cytometry. Cell proliferation and extracellular alkaline phosphatase secretion were detected by BrdU and alkaline phosphatase ELISA kits. The mRNA expression level of osteoblast related gene was detected by Real-time PCR. Results Compared with the control group, the result of treatment groups with increasing mistletoe polysaccharose concentrations were as follows: the proportions of S phase and G₂/M phase in cell cycle increased and the cell count Annexin Ⅴ+/PI-significantly decreased, the number of cells increased, extracellular alkaline phosphatase activity obviously decreased. The increasing transcription levels of Runtrelated transcription factor 2(Runtx2) and collagen typeⅠ alpha 1(COL1A) were stabled over 2.5 g/L and the upregulation of mRNA expression of osteocalcin (OC) was steady at 1.25 g/L. Conclusion Mistletoe polysaccharose can promote the proliferation and inhibit the apoptosis of MC3T3-E1 cells, and its possible mechanism might be related to down-regulating of extracellular alkaline phosphatase activity and the grow exhanced expression of OC, Runtx2 and COL1A.