Objectives: The aim of this study was to investigate the effect and potential mechanism of Cysteine-rich 61 (Cyr61) on stimulating MMP-3 expression by fibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA) patients.Methods: Primarily cultured RA FLS were treated with exogenous Cyr61 protein or Cyr61-siRNA, then, MMP-3 expression was analyzed by real-time PCR, western blotting and ELISA. Signal transduction pathways in Cyr61-induced MMP-3 production were examined by real-time PCR, western blotting, confocal microscopy, luciferase reporter assay. Mice with collagen-induced arthritis (CIA) were treated with anti-Cyr61 monoclonal antibodies (mAb), or IgG1 as control and MMP-3 in the joint was detected by IHC, real-time PCR and western blotting.Results: High expressed MMP-3 and Cyr61 were positively correlated in RA ST; Cyr61 stimulated MMP-3 production in FLS of RA patients in an IL-1 and TNF- independent manner. Cyr61 induced MMP-3 could further enhance the invasive ability of RA FLS. Mechanistically, we found that Cyr61 promoted MMP-3 production via the P38, JNK-dependent AP-1 signaling pathway. Blockage of Cyr61 function with monoclonal antibody could decrease MMP-3 expression in the joints of CIA mice.Conclusion: This study provides new evidence that Cyr61 participates in RA pathogenesis not only as a pro-inflammatory factor but also plays a key role in bone erosion via promoting MMP-3 expression. We suggest that targeting of Cyr61 may represent a potential strategy in RA treatment.