Rheumatoid arthritis (RA) is characterized by hypertrophic synovial tissues comprising excessively proliferating synovial fibroblasts and infiltrating inflammatory cells. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that regulates cell growth, inflammation and angiogenesis by acting on various cell types. In RA synovial tissues, TGF-beta is expressed at high levels. However, the precise role of TGF-beta in RA remains unclear. We herein demonstrated a causal link between the TGF-beta-induced RA synovial cell proliferation and induction of platelet-derived growth factor (PDGF)-AA. In addition, TGF-beta induced IL-6 and vascular endothelial growth factor (VEGF) production by RA synovial fibroblasts associated with nuclear factor-kappa B activation. These effects of TGF-beta on RA synovial fibroblasts were suppressed by TGF-beta type I receptor kinase inhibitor HTS466284. Furthermore, HTS466284 significantly prevented anti-collagen type II antibody-induced arthritis in mice according to the clinical manifestations, histology, tumor necrosis factor-alpha, PDGF and VEGF expression and 5-bromo-2'-deoxyuridine incorporation. These in vitro and in vivo results suggest that TGF-beta plays a role in the development of synovial hyperplasia consisting of synovial cell proliferation, inflammation and angiogenesis. The blockade of TGF-beta signaling may thus become an additional strategy for the treatment of RA.