Aim To investigate the protect function of clopidogrel on blood vessel endothelium in patients with coronary heart disease(CHD). Method 166 patients with CHD confirmed by coronary arteriography were randomly divided into two groups.At the first six months the two groups were all treated with clopidogrel and aspirin.At the last six months the control group were only treated with aspirin and the case group continued with clopidogrel and aspirin(other foundation medicine in CHD were the same at the two groups).Compliance and endothelial function of brachial artery were determined by pulsed Doppler technique at 6th month and 12th month.Brachial artery diastolic diameter(Dd),mean flow velocity(Vm),blood flow volume(Q),distensibility(DC),resistance of blood flow(R) and intima-media thickness(IMT) were used as the indexes of compliance of brachial artery.While the brachial artery diastolic diameter(Dd'),the mean flow velocity(Vm'),the blood flow volume(Q') and the resistance of blood flow(R') after brachial artery reactive hyperaemia were used as the indexes of endothelial function of it. Results At the case group,the brachial artery diastolic diameter,mean flow velocity,blood flow volume and distensibility increased,resistance of blood flow and IMT cut down,and there were significant changes in 12th month vs 6th month.There were significant changes between the case group and the control group in improving the function of blood vessel endothelium at 12th month.At the case group,the brachial artery diameter,flow velocity,blood flow volume increased in artery reactive hyperaemia test and resistance of blood flow cut down.At the control group,the brachial artery diameter,blood flow volume and resistance of blood flow did not change in 12th month vs 6th month. Conclusion Long-term treatment with clopidogrel may improve the compliance and endothelial function of blood vessel endothelium.