This study was to investigate the functional role of RNA methyltransferase METTL3, an enzyme catalyzes the formation of N6-methyladenosine (m6A) on the target mRNA, in the development of osteoarthritis (OA) and the underlying mechanism. Cytokine IL-1β was used to stimulate the chondroprogenitor cell line ATDC5 cells to mimic the inflammatory condition in vitro. The level of METTL3 mRNA and m6A as well as inflammatory cytokines were detected by qRT-PCR. Cell activity was detected by CCK-8. The rate of apoptotic cell was measured by flow cytometry. Western blot was used to detect the levels of NF-κB signaling molecules and collagen in cells. Methylation inhibitor cycloleucine and methyl donor betaine were used to treat collagenase-induced OA mice. In IL-1β-treated ATDC5 cells, the METTL3 mRNA levels and the percentage of m6A methylated mRNA of total mRNA were increased in a dose-dependent manner. Silencing of METTL3 by shRNA reduced the percentage of IL-1β-induced apoptosis, suppressed IL-1β-induced increased inflammatory cytokines levels and activation of NF-κB signaling in chondrocytes. Moreover, silencing of METTL3 promotes degradation of extracellular matrix (ECM) by reducing the expression of MMP-13 and Coll X, elevating the expression of Aggrecan and Coll II. In a OA mouse model induced by collagenase, injection of methylation inhibitor cycloleucine or methyl donor betaine does not affects METTL3 mRNA expression, but significantly inhibits or promotes the total level of m6A as well as inflammatory condition and ECM degradation, respectively. METTL3 has a functional role in mediates osteoarthritis progression by regulating NF-κB signaling and ECM synthesis in chondrocytes that shed insight on developing preventive and curative strategies for OA by focusing on METTL3 and mRNA methylation. •METTL3 levels and m6A methylated mRNA were increased in IL-1β-treated ATDC5 cells.•Silencing of METTL3 promotes degradation of extracellular matrix by reducing the expression of MMP-13 and Coll X.•Methylation inhibitor significantly inhibits the total level of m6A as well as inflammatory condition and ECM degradation.•METTL3 promotes osteoarthritis progression by regulating NF-κB signaling and ECM synthesis in chondrocytes.