BACKGROUND The aim of this study was to explore the effects of NADPH oxidase 5 (NOX5) in high glucose-stimulated human glomerular mesangial cells (HMCs). MATERIAL AND METHODS Cells were cultured under normal glucose (NG) or high glucose (HG) conditions. Then, NOX5 siRNA was transfected into HG-treated HMCs. A Cell Counting Kit-8 assay, colony formation assay and 5-ethynyl-20-deoxyuridine (EDU) incorporation assay were applied to measure cell proliferative ability. In addition, the levels of oxidative stress factors including reactive oxygen species (ROS), malonaldehyde (MDA), NADPH, superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX), inflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, IL-1ß, and monocyte chemoattractant protein-1 (MCP-1) in HMCs were detected by kits. Moreover, the expression of TLR4/NF-kappaB signaling and extracellular matrix (ECM) associated genes were evaluated by western blotting. RESULTS The results revealed that the NOX5 was overexpressed in HG-treated HMCs. Silencing of NOX5 decreased proliferation of HMCs induced by HG. And NOX5 silencing alleviated the production of MDA and NADPH accompanied by an increase of SOD and GSH-PX levels. Additionally, the contents of TNF-alpha, IL-6, IL-1ß, and MCP-1 were reduced after transfection with NOX5 siRNA. Furthermore, silencing of NOX5 deceased the expression of collagen I, collagen IV, TGF-ß1, and fibronectin induced by HG stimulation. TLR4, MyD88, and phospho-NF-kappaB p65 expression were downregulated notably in NOX5 silencing group. CONCLUSIONS Taken together, these findings demonstrated that inhibition of NOX5 attenuated HG-induced HMCs oxidative stress, inflammation, and ECM accumulation, suggesting that NOX5 may serve as a potential therapeutic target for diabetic nephropathy (DN) treatment.