Abstract: Objective To study the inhibitory effect of recombinant RANK protein on absorption activity of osteoclasts in vitro. Methods Mouse osteoblasts and RAW₂64.7 cells were cocultured in 6-well plates at the ratio of 4 to 1 for 6 days.The cells were stained with tartrate-resistant acid phosphatase（TRAP）.Three days after recombinant RANK protein was added at the concentrations of 10^-4g/L,10^-5g/L and 10^-6g/L and the control was set,the quantity and morphology of osteoclasts were observed,TRAP-positive cells in each unit area and bone absorption pits were counted. Results Six days after culture,a large number of multinuclear mature osteoclasts were formed,and TRAP staining confirmed them to be mature osteoclasts.Three days after recombinant RANK protein was added,the number of TRAP-positive osteoclasts and bone absorption pits was significantly lower in the experimental group than in the control group. Conclusion Recombinant RANK protein can effectively inhibit the differentiation and bone absorption of osteoclasts in vitro.