Abstract： Objective To study the relationship between insulin resistance and vascular endothelial dysfunction in obese children. Methods A total of 176 obese children, 58 over-weight children and 45 healthy children were recruited. All the participants underwent hematologjc tests. Homeostasis model of assessment of insulin resistance ( HOMA-IR) and insulin sensitivity index were calculated. Ultrasound measurement was used to investigate carotid intima-media thickness ( IMT) and carotid artery compliance (CAC). Results There were significant difference among the three groups in risk factors of atherosclerosis, subclinical inflammation, IMT ( F = 3. 209, P = 0. 046 ), and CAC ( F = 6. 576, P = 0. 002 ) . In sulin sensitvity index was correlated with adiponectin (R = 0. 419, P = 0. 000) , risk factors of atherosclerosis, soluble intercellular adhesion molecule 1 (R= -0. 201 ,P = 0. 010) ,and IMT (R= -0. 201 ,P = 0. 010). The risk factors of atherosclerosis and vascular damage were increased as in sulin sensitvity index decreased. Multiple stepwise regression analysis revealed strong relationship between IMT and abdominal obesity, mean blood pressure, HOMA-IR and high-density lipoprotein cholesterol. Conclusion Early atherosclerosis may develop in obese children. Prevention of childhood obesity should be important in the prevention of adult cardiovascular and cerebrovascular diseases.