Objective In order to probe other possible mechanisms of aerobic tra ining in anti-atherosclerosis besides lipid-regulation, we observed the influenc e of aerobic training on the formation of atherosclerotic plaque, the concentrat ion of nitric oxide(NO) in serum, the content of inducible nitric oxidase (iN OS) and endothelial nitric oxidase (eNOS) in thoracic aorta in ApoE-deficient mi ce. Methods The atherosclerotic lesions, the serum NO, the con tent of thoracic aortic iNOS and eNOS by ABC immunohistochemical staining combin ed with computer image quantitative analysis technique on frozen sections were m easured after 10-week swimming training. Thoracic aorta Oil Red O (ORO) staining on the intima were als o analyzed. Results Compared with controls, aerobic training d elayed the plaque formation i n ApoE-deficient mice (P