OBJECTIVE: The aim of this study was to explore the functional role of LAMP3-mediated epithelial-mesenchymal transition (EMT) in fibroblast-like synoviocytes (FLSs) in rheumatoid arthritis (RA) patients and to evaluate its potential as a therapeutic target. METHODOLOGY: Changes in EMT and LAMP3 were investigated in the synovial tissue and FLSs of RA patients. In vitro experiments were performed using the EMT inhibitor C19, siRNA, and lentivirus to examine the impact of EMT and LAMP3 on RA-FLSs and the underlying mechanisms involved. Finally, C19 was administered to mice with collagen-induced arthritis (CIA) to validate the therapeutic efficacy of C19 in treating arthritis. RESULTS: Compared with patients with osteoarthritis (OA), RA patients exhibited increased EMT and increased expression of LAMP3 in the synovium. The results from the in vitro experiments demonstrated that inhibiting EMT effectively reduced the excessive proliferation, anti-senescent properties, migration, and invasive behavior of RA-FLSs, as well as the secretion of MMP1, MMP3, and MMP13. Additionally, regulating the expression of LAMP3 not only affected the EMT pathway but also impacted the excessive proliferation and invasive behavior of RA-FLSs. In the CIA model, administration of the EMT inhibitor C19 significantly alleviated the progression of arthritis. CONCLUSION: These findings demonstrate the inhibitory impact of EMT on arthritis and suggest that inhibiting EMT or LAMP3 may be a promising novel therapeutic approach for treating RA.