Objective To compare the condition of the structure and oxidative stress of great saphenous vein grafts between the patients with and without type 2 diabetes mellitus, and to study the mechanisms for providing the theory evidence ofthe protective way for great saphenous vein graft in patients with type 2 diabetes mellitus. Methods The segments of human great saphenous vein graft were collected from 36 patients undergoing coronary artery bypass graft surgery, who were divided into 2 groups, experimental group (17 patients with type 2 diabetes mellitus) and control group (19 patients without type 2 diabetes mell itus). There was no significant difference in age, gender, hypertension, serum creatinine, hyperl ipidemia, smoking, and the number of pathological coronary arteries between 2 groups (P gt; 0.05). Two cm distal great saphenous vein from each patient was obtained. The structure of great saphenous vein was observed by the microscope, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzymatic activity and superoxide anion level were quantified by lucigenin-enhanced chemilumi nescence. Results The NADPH oxidase activity and superoxide anion levels were significantly higher in experimental group [(308.8 ± 33.7) counts/μg and (1 951.71 ± 355.2) counts/(min.mg)] than in control group [(202.7 ± 29.5) counts/μg and (1 230.73 ± 340.5) counts/(min.mg)] (P lt; 0.05). HE staining showed the damage of ultrastructure of great saphenous vein endothel ium in experimental group, including necrosis and exfol iation of endoepithel ial cells, spl itting of the basement membrane, thickened lower layer of the endothelium with vacuoles and deformed vascular smooth muscle cells; however, integrated vessel intima was observed in control group.