The aim of this study was to investigate the effects of soy isoflavones on the injury of human umbilical vein endothelial cells induced by H2O2. EVC‑304 cells were preincubated with soy isoflavones for 12 h, and then exposed to 100 µM H2O2 for 1 h. Cell viability was evaluated by a 3‑(4,5‑di‑methylthiazol‑2‑yl) 2,5‑diphenyltetrazolium bromide assay. The apoptosis of EVC‑304 cells was detected by Hoechst 33258 and Annexin‑V/propidium iodide staining. The oxidative stress‑related biochemical parameters were detected and the expression of apoptosis‑related proteins was examined by western blot analysis. The results showed that incubation with soy isoflavones caused a significant increase in the viability of EVC‑304 cells and a decrease in cell apoptosis induced by H2O2. Soy isoflavones also markedly enhanced the activities of superoxide dismutase and glutathione peroxidase, and reduced the level of malondialdehyde. Western blot analysis results show that soy isoflavones can modulate the activation of nuclear factor‑κB and the mitochondria‑mediated apoptosis signaling pathway. The results of this study indicated the potential biological relevance of soy isoflavones in the therapy of cardiovascular diseases.