Objective To investigate the role and mechanism of RSPO1 in osteoblasts differentiation.Methods The xCELLigence system was used to study the toxicity and role of RSPO1 on the C2C12 cells proliferation.Alkaline phosphatase (ALP) activity was measured by using a phosphatase detection kit.The expression of osteoprotegerin (OPG) was determined using enzyme-linked immunosorbent assay (ELISA).Wnt/β-catenin signaling was evaluated using the TOPflash T cell factor (TCF) luciferase reporter assay.Western blotting assay was performed to confirm the accumulation of β-catenin protein.T test was used for statistical analysis.Results RSPO1 had no effect on the C2C12 cells proliferation,and it produced no toxicity to C2C12 cells.RSPO1 alone resulted in a slight increase in the activity of ALP (2.85±0.08 vs 1.74±0.21,t=3.014,P＜0.05) and the expression of OPG (1.29±0.13 vs 1.00±0.21,t=3.348,P＜0.05),whereas the combination of RSPO1 and Wnt3A significantly amplified ALP activity (81.37±5.08 vs 1.74±0.21,t=31.31,P＜0.01) and OPG protein expression (5.26±0.60 vs 1.00±0.21,t=6.99,P＜0.01).RSPO1 synergized with Wnt3A to activate TCF activity and induce accumulation of β-catenin (3.28±0.18 vs 1.00±0.21,t=10.94,P＜0.05).However,RSPO1 alone had no effect on the TCF activity and β-catenin accumulation (1.25±0.08 vs 1.00±0.21,t=2.225,P＞0.05).Conclusion Our study has revealed that RSPO1 synergized with Wnt3A in activating Wnt/β-catenin signaling pathway to induce osteoblasts differentiation,which demonstrate the therapeutic potential of RSPO1 for RA.