It has previously been demonstrated that nicotinamide adenine dinucleotide phosphate?oxidase (NADPH) oxidase?4 (Nox4), is important in the pathogenesis of diabetic nephropathy (DN), however the exact mechanisms remain to be elucidated. The present study aimed to examine the effect of Nox4 on the alteration of the Notch pathway and cell apoptosis in the renal tubular epithelial cell line, HKC, under conditions of high glucose (HG; 30?mmol/l glucose). Nox4 and the Notch pathway were inhibited by N?acetylcysteine (NAC), diphenylene iodonium (DPI) or γ?secretase inhibitor (DAPT). The protein levels of Nox4, Notch1, Notch intracellular domain?1 (NICD1), phosphorylated (p) Ras?related C3 botulinum toxin substrate?1 (Rac1), Rac1, B?cell lymphoma 2 apoptosis regulator (Bcl?2), Bcl?2 associated protein X apoptosis regulator (Bax) and cleaved caspase?3 were determined by western blotting. The Nox4 and Notch1 mRNA levels were detected by reverse transcription?quantitative polymerase chain reaction. Intracellular reactive oxygen species (ROS) levels were detected via chloromethyl?2',7'?dichlorodihydrofluorescein diacetate. Apoptotic cells were determined using an Annexin V/propidium iodide apoptosis detection kit. HG upregulated Nox4, Notch1, NICD1, p?Rac1, Bax and cleaved caspase?3 expression levels and downregulated Bcl?2 expression in cultured HKC cells, compared with cells cultured in normal glucose levels. Inhibition of the Notch pathway via DAPT increased Bcl?2 expression, decreased Bax and cleaved caspase?3 levels and prevented HKC cell apoptosis. Inhibition of Nox4 by NAC and DPI inhibited the Notch signaling pathway and ROS generation, which prevented HKC cell apoptosis. These findings indicated that Nox4 potentially mediates HG?induced HKC cell apoptosis via the Notch pathway, and may be involved in renal tubular epithelial cell injury in DN.