〔Abstract〕 Objective To investigate the effects of Dendrobium candidum polysaccharide on the differentiation of bone marrow-derived macrophages cells(BMMs) into osteoclasts induced by receptor activator of nuclear factor-κ B ligand(RANKL)in vitro. Methods Water extraction and alcohol precipitation method was used to extract the Dendrobium polysaccharide from Dendrobium candidum. C57 BL/6 mouse BMMs were induced by macrophage colony-stimulating factor(M-CSF). The effects of different concentrations of Dendrobium polysaccharide on the proliferation and cell viability of mouse BMMs were detected by CCK-8 method. The expressions of p65, phospho-p65(p-p65), p38, phospho-p38(p-p38), nuclear factor of activated T-cells cytoplasmic 1(NFATc1) and c-Fos was detected by Western blot. The expression of tartrate-resistant acid phosphatase(TRACP), NFATc1, Cathepsin K(CTSK) and matrix metalloproteinase-9(MMP9) gene were detected by qRT-PCR. The BMMs were induced by RANKL and different concentrations of Dendrobium polysaccharide to carry out TRACP staining. Results When the polysaccharide concentration of Dendrobium candidum reached 400 μg/ml, it significantly inhibited the proliferation of BMMs(P<0.05). Western blot showed that Dendrobium candidum polysaccharide reduced the expression of NFATc1, c-Fos protein, decreased the phosphorylation levels of p65 and p38, which showed a dose-dependent effect(P<0.05). qRT-PCR showed that compared with the RANKL-induced group, the expression of NFATc1, MMP9, CTSK and TRACP genes of Dendrobium polysaccharide group were down-regulated(P<0.05). The TRACP staining showed that the formation of osteoclasts with relatively large volume and>10 nucleus was observed in the RANKL-induced group. The formation of osteoclasts in the concentration of 200 μg/ml was inhibited and only a small number of immature osteoclasts with relatively small volume were formed. Conclusion In vitro, Dendrobium candidum polysaccharide inhibits the expression of osteoclast-associated genes and the synthesis of related pathway proteins, inhibiting RANKL-induced osteoclast differentiation of BMMs.