Aim To explore the influence of acute glucose loading on endothelium-dependent vasodilation in essential hypertension and the protective effect of vitamin C and vitamin E. Methods 39 patients with essential hypertension (EH) and 21 normaltensive controls were randomly divided into three groups. We evaluated the acute effects of oral glucose loading(75 g) alone, with Vitamin C (2 g) and E (0.8 g) or Vitamin C (0.9 g) on endothelium-dependent flow-mediated dilation (EDF) of the brachial artery assessed by high-resolution ultrasound technique on 0,1,2,3 hour after glucose loading respectively. At the same time, we measured the concentrations of plasma superoxide dismutase (SOD), total antioxidative capacity (T-AOC) and superoxide anion (O 2 -). Results The basic EDF were diminished in EH. After 75 g glucose loading, EDF were decreased significantly in both patients (9.48%±3.33% vs 13.09%±6.78%, p<0.05) and controls (14.20%±6.48% vs 17.91%±6.87%, p<0.05). The severity of postprandial EDF was more serious in EH than in controls groups (9.48%±3.33% vs 14.20%±6.48%, p<0.05). The impairment was most significant in the first hour and returned to the basic level in the second hour. Different dose of vitamins can improve the impairment in a dose-dependent manner. Conclusions EDF impairment was induced by acute hyperglycemia in EH patients which can be reversed by high concentration of vitamin C and vitamin E.