A disintegrin and metalloproteinase 12 (ADAM12) is known to be involved in chondrocyte proliferation and is upregulated in the synovial tissue of osteoarthritis (OA). However, the underlying mechanisms of ADAM12 on rheumatoid arthritis (RA) synovial cell proliferation remain unknown. Here, we investigated the role of ADAM12 in the proliferation of RA synovial fibroblasts (RASFs). The expression and localization of ADAM12 in RA synovial tissues were examined by immunohistochemistry and compared with OA and healthy control (HC) synovial tissues. The effect of inflammatory cytokines (TNF-α, TGF-β1, and PDGF-BB) on ADAM12 expression in RASFs from RA patients was examined by real-time RT-PCR. The effect of ADAM12 knock-down by ADAM12 siRNA and ADAM12 overexpression on cell proliferation of RASFs were examined by WST-1 assay. ADAM12 was identified predominantly in RA synovial tissue rather than OA and HC synovial tissues. Stimulation with TGF-β1 upregulated the expression of ADAM12 and cell proliferation of RASFs. ADAM12 siRNA suppressed TGF-β1-induced cell proliferation of RASFs, while ADAM12 overexpression promoted the cell proliferation of RASFs. These findings demonstrate that ADAM12 may have a key role in TGF-β1-induced cell proliferation of synovial fibroblasts in patients with RA.