Oxidative injury of vascular endothelial cells in the initial event of atherosclerosis (AS) in diabetes was assessed in the present study. The antioxidant effect of oleanolic acid (OA) has attracted much attention. In the present study the potential effects of OA on human umbilical vein endothelial cells (HUVECs) were investigated. Cell viability was examined using the CCK‑8 assay. The activity of oxidative stress parameters was determined using commercial kits. Flow cytometry analysis was performed to detect the level of reactive oxygen species (ROS), mitochondrial membrane potential (MMP) and cell apoptosis. The expression levels of target genes and proteins were examined by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blot analysis. It was indicated that cell viability that was suppressed by high glucose was increased by the pretreatment of OA, and nitric oxide (NO) generation, the activities of superoxide dismutase (SOD) and catalase (CAT) were recovered by OA. By contrast, it was observed that OA decreased the MDA content. Notably, the pretreatment of OA alleviated mitochondria damage by reducing the level of ROS and maintaining MMP. In addition, apoptosis that was caused by high glucose was reduced by OA. Pro‑apoptotic genes (caspase‑3, Fas, Fasl) and anti‑apoptotic gene (Bcl‑2) expression levels were decreased and increased in the OA groups, respectively. Furthermore, the activity of AKT/endothelial nitric oxide synthase (eNOS) signaling was elevated by OA. Taken together, it was suggested that OA could protect against oxidative stress‑induced apoptosis of HUVECs, which was associated with AKT/eNOS signaling pathway.