〔Abstract〕 Objective Dendrobium polysaccharide(DOP-1-1) was prepared and its effects on the proliferation, differentiation and mineralization of pre-osteoblast MC3 T3-E1 cells were investigated. Methods A homogeneous polysaccharide(DOP-1-1) was obtained from Dendrobium officinale polysaccharide(DOP) through systematic separation and purification, and the structure of DOP-1-1 was studied by high-performance gel permeation chromatography, monosaccharide analysis, infrared spectroscopy, methylation analysis, GC-MS and NMR spectroscopy.In vitroexperiments were performed to detect the effects of DOP-1-1 on the proliferation, differentiation and mineralization of MC3 T3-E1 cells by MTT method, ALP activity determination and Alizarin Red S staining. At the same time, Western blot was used to determine the effect of DOP-1-1 on the expression of bone-related proteins(Pin1, BMP2, RUNX2) in MC3 T3-E1 cells. Results DOP-1-1 was a homogeneous polysaccharide with relative molecular weights of 3 611, which was composed of mannose, glucose and galactose. DOP-1-1 had excellent activity of promoting osteoblast proliferation in a low concentration, and the effects of 2.0 and 4.0 μmol/L of DOP-1-1 were equivalent to Positive Control 17β-estradiol(E2). Compared with the control group, E2 and DOP-1-1(4.0, 8.0 μmol/L) increased the ALP activity and mineralization rate in MC3 T3-E1 cells(P<0.01). In particular, the ALP activity and mineralization rate of DOP-1-1(8.0 μmol/L) were higher than those of the positive control E2(P<0.001). In addition, the expression of Pin1, BMP2, and RUNX2 protein in MC3 T3-E1 cells in the DOP-1-1 group was higher than that in the control group(P<0.05). Conclusion DOP-1-1 can promote the proliferation, differentiation and mineralization of MC3 T3-E1 cells in vitro, and its mechanism is related to the activation of Pin1/BMP2 signaling pathway.