Aim To explore the effect of aerobic exercise on endothelial function in elderly spontaneously hypertensive rats (SHR), and the oxidative stress mechanism. Methods Sixteen-month-old male spontaneously hypertensive rats (n＝24) and male Wistar Kyoto rats (WKY, n＝24) with the same age were selected. Wistar Kyoto rats and spontaneously hypertensive rats were randomly assigned to sedentary control groups (WKY-C and SHR-C) and exercise-trained groups (WKY-EX and SHR-EX), seperately. The animals in exercise-trained groups ran on a motor treadmill (0° slope, 5 d/w, 60 min/d) at 16~18 m/min for 8 weeks. Blood pressure was examined by non-invasive methods, isolated vessel rings were applied to evaluate vasomotor response, plasma samples were used for measurement of NO level and relative oxidative stress markers. Results The systolic blood pressure was significantly lower in SHR-EX group than that in SHR-C group (P＜0.05). Serum malondialdehyde (MDA) in SHR-EX group (7.9±0.3 μmol/L) was lower than that in SHR-C group (11.8±1.0 μmol/L, P＜0.05), serum MDA in SHR-C group was significantly higher than that in WKY-C group (7.2±0.3 μmol/L, P＜0.05). Antioxidant enzymes including glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD), however, there was no significant difference between four groups. Exercise had significant changes of NE-induced vascular contraction in SHR (SHR-EX:136.0±1.8 %KMAX; SHR-C:153.2±1.9 %KMAX, P＜0.05). Compared with SHR-C group, NE-induced vascular constriction in WKY-C group (120.2±5.6 %KMAX, P＜0.05) were significantly lower, and that in WKY-EX group (143.9±4.3 %KMAX) were significantly higher than that in WKY-C group (P＜0.05). Endothelium-dependent vasodilaton in SHR-C group (50.2±2.8 %NE) was significantly lower than that in WKY-C group (100.1±0.6 %NE, P＜0.05), endothelium-dependent vasodilaton in SHR-EX group (97.0±1.5 %NE) was significantly higher than that in SHR-C group (P＜0.05). After 15 min incubation with NADPH oxidase inhibitor Apocynin in vitro, endothelium-dependent vasodilaton in SHR-C group (98.6±1.3 %NE) significantly increased. NO-dependent vasodilation in SHR-C group (25.5%±2.3%) was significantly lower than that in WKY-C group (85.2%±0.7%, P＜0.01), NO-dependent vasodilation in SHR-EX (86.8±3.4%) and WKY-EX(98.8±1.5%) was significantly higher than the corresponding control group (P＜0.05). Conclusion Long-term aerobic exercise inhibits the increase of oxidative stress and the decrease of NO bioavailability induced by aging and/or hypertension and improves vascular endothelial dysfunction.