Osteoarthritis (OA) is a common and frequently-occurring disease in middle-aged and older people. A growing number of studies have shown that microRNAs (miRNAs) are involved in the development of OA. However, the role and mechanism of miR-33b-3p in OA remain ill-defined. The levels of miR-33b-3p and DNA methyltransferase 3A (DNMT3A) mRNA were determined by quantitative real-time polymerase chain reaction (qRT-PCR). The levels of DNMT3A protein, matrix metalloprotein 13 (MMP-13), a disintegrin and metalloproteinase with thrombospondin motif-5 (ADAMTS-5), collagen II, aggrecan, cleaved Caspase-3, B-cell lymphoma-2 (Bcl-2) and BCL2-Associated X (Bax) were measured by Western blot assay. Cell proliferation and cell apoptosis were assessed by Cell Counting Kit-8 (CCK-8) assay and flow cytometry analysis, respectively. The targeting relationship between miR-33b-3p and DNMT3A was verified by dual-luciferase reporter assay. The expression of miR-33b-3p was decreased and the expression of DNMT3A was increased in OA cartilage tissues and IL-1 beta-induced chondrocytes. There was an inverse correlation between miR-33b-3p and DNMT3A in OA cartilage tissues. MiR-33b3p overexpression or DNMT3A knockdown inhibited extracellular matrix (ECM) degradation and cell apoptosis and promoted cell proliferation in IL-1 beta-induced chondrocytes. Moreover, DNMT3A was confirmed to be a direct target of miR-33b-3p. Upregulation of DNMT3A weakened the effects of miR33b-3p overexpression on cartilage ECM degradation, cell proliferation and apoptosis in IL-1 beta-activated chondrocytes. MiR-33b-3p overexpression suppressed cartilage ECM degradation and cell apoptosis, and promoted cell proliferation by directly targeting DNMT3A in IL-1 beta-stimulated chondrocytes. (C) 2019 Elsevier Inc. All rights reserved.