The aim of this study was to investigate the effects of onion (Allium cepa) extracts (ACE) on doxorubicin (DOX)-induced apoptosis in aortic endothelial cells. The rats in the ACE-pretreated group were given a daily dose of 1 ml ACE for 14 days. To induce aortic endothelial cell apoptosis, DOX (30 mg kg−1 body weight) was injected intraperitoneally by a single dose and the rats were sacrificed after 48 h. To date, no such studies have been performed on antiapoptotic potential of ACE on DOX-induced apoptosis in aortic endothelial cells. Our data indicate a significant reduction in the activity of in situ identification of apoptosis using terminal dUTP nick end-labeling in aortic endothelial cells of the DOX-treated group with ACE therapy. DOX-treated with ACE groups showed a significant decrease in malondialdehyde levels and increased levels of glutathione in comparison with the DOX-treated group. Data from our study show that prevention of endothelial cell apoptosis by ACE may contribute to the restoration of aortic endothelial dysfunction that is associated with DOX treatment. Copyright © 2011 John Wiley & Sons, Ltd.