This study is to examine the effects of equol on the H2O2-induced death of bovine aortic endothelial cells (bAECs) and the mechanism of its protective effects. MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] assay showed that in the control group, cell survival Fate decreased significantly, each in proportion to the duration of the H2O2 Stimulation (P < 0.05), but, in the equol-pretreated group, such decrease was not statistically significant. After Hoechst 33342 staining, in the equol-pretreated group the number of cells with apoptotic morphology decreased significantly. Equol pretreatment effectively inhibited the H2O2-induced cell death by the reduction of intracellular ROS production (P < 0.05). Incubation of bAECs with equol increased the expression of phospho-p38 MAPK and Bcl-2 after the H2O2 exposure compared with their expression without the equol pretreatment. Furthermore, SB203580 inhibited phospho-p38 MAPK expression and increased apoptotic cell death. This Study proves equol has a significant antioxidant effect on the bAECs that were exposed to H2O2. (C) 2008 Elsevier Inc. All rights reserved.