Purpose: The prevalence of obesity in children is increasing rapidly. Epidemiologic studies suggest that obesity induced atherosclerosis may start in childhood. We investigate whether overweight children show early abnormalities of the arterial wall and endothelial dysfunction. Methods: Thirty-eight obese children (age 14, male, BMI 29.40짹3.18) and forty-five age, sex-matched healthy control children (BMI 18.43짹1.01) were enrolled. The carotid artery intima-media thickness (IMT) and brachial artery flow-mediated dilation (FMD) response were measured by high-quality ultrasound system, and compliance, distensibility, stiffness index, incremental elastic modulus, and wall stress were calculated by equation. In addition, we looked the relation between these arterial features and metabolic cardiovascular risk factors. Results: The obese children had significantly increased IMT (0.52짹0.09mm vs 0.40짹0.07mm, P<0.001) and markedly impaired FMD (7.35짹7.78% vs 20.34짹16.81%, P<0.001) than the healthy controls. But the compliance, distensibility were non-significantly lower and stiffness index, incremental elastic modulus, wall stress were non-significantly higher in obesity group. BMI was highly associated with increased IMT (r=0.216, P <0.001) and reduced FMD (r =-0.520, P <0.001), as were blood levels of total cholesterol, LDL cholesterol and Apolipoprotein B. Conclusions: Childhood obesity seems to contribute to the development and progression of arterial wall changes and endothelial dysfunction. Ultrasonography of the arterial wall may be used in a clinical setting to identify high-risk patients among obese children.