Aim To study the relationship between endothelium-dependent vasodilatation in abdominally obese patients and serum leptin. Methods The patients were matched into abdominally obese group and controll group according to age and sex.The concentration of leptin was assayed by radioimmunoassay.The endothelium-dependent vasodilatation was measured by high-resolution ultrasound in the two groups. Results The brachial flow-mediated vasodilatation in abdominally obese group was much lower compared with that in control group(6.71%±3.60% vs 13.81%±3.71%,p<0.01).However,there was no significant difference in response to nitroglycerin between the two groups(19.71%±6.63% vs 18.60%±6.35%,p>0.05).The concentration of serum leptin in abdominally obese group was much higher than that in control group,the obese male vs the controlled male is 8.63±3.73 μg/L vs 3.05±1.56 μg/L(p<0.01);the obese female vs the controlled female is 16.73±6.93 μg/L vs 7.93±3.66 μg/L(p<0.01).The brachial flow-mediated vasodilatation was negatively correlated with the concentration of serum leptin according to Pearson correlation analysis. Conclusions The endothelium-dependent vasodilatation dysfunction in abdominally obese patients is negatively correlated with the increase of the concentration of serum leptin.