β-Catenin is the key mediator of the Wnt signal and also a component of E-cadherin complexes at the intercellular adhering junction, which mediates cell-cell adhesion. We hypothesized that β-catenin might be involved in the long-lasting changed phenotype of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) and could play a role in the pathogenesis of RA. In this study we investigated the expression of β-catenin in RA-FLS.