Aim To study vascular endothelial function in patients with metabolic syndrome and relationship between risk factors and endothelial function. Methods Brachial artery vascular diameter and blood flow volume were measured after reactive hyperemia and nitroglycerin sublingual nitroglycerin respectively in 35 patients with metabolic syndrome and 21 subjects as normal control by high-resolution ultrasonography. Results There were significant differences of triglyceride, fasting blood glucose (FBG),postprandial blood glucose (PBG), systolic blood pressure (SBP), diastolic blood pressure (DBP) and body mass index (BMI) between control group and metabolic syndrome group (p<0.05 or p<0.01). There were significant differences of percentage of the brachial artery diameter change of reactive hyperemia,percentage of the diameter change of nitroglycerin sublingual administration and percentage of flow volume change of nitroglycerin sublingual administration (p<0.05 or p<0.01). Endothelium-dependent dilatation in patients with metabolic syndrome was significantly negatively related with age (r=-0.29, p<0.05), triglyceride (r=-0.38, p<0.05), SBP (r=-0.71, p<0.01), DBP (r=-0.61, p<0.01), FBG (r=-0.62, p<0.01), PBG (r=-0.66, p<0.01) and BMI (r=-0.47, p<0.05) respectively. Conclusions Dysfunction of endothelium-dependent and endothelium-independent dilatation in patients with metabolic syndrome are apparent. Endothelium-dependent dilatation was significantly negatively related with age, triglyceride, blood pressure, blood glucose and body mass index.