Aim To investigate the structure and function of carotid artery and endothelial function in patients of acute coronary syndrome with high-frequency ultrasound. To study the relation of atherosclerosis and acute coronary syndrome. Methods With high-frequency ultrasound, not only intimal-medial thickness (IMT), plaque of carotid arteries, but also endothelium-dependent relaxing function of brachial artery were measured in subjects with acute coronary syndrome, stable angina pectoris and controls. Results IMT and endothelium-dependent relaxing function in acute coronary syndrome group (0.10±0.02 and 3.98±1.65) and stable angina pectoris group (0.11±0.04 and 4.76±2.37) were significantly higher than those in controls (0.07±0.01 and 9.33±3.47)(p<0.05). Plaque scores, plaque index in acute coronary syndrome group (4.06±2.21 and 3.14±1.97) were not significantly higher than those in stable angina pectoris group (4.17±1.76 and 3.21±1.88) (p>0.05). Unstable plaques were more common than stable plaques in acute coronary syndrome. Conclusion Peripheral blood vessel sonophic examination can measure athersclerosis. The structure and function of carotid artery and endolial function were associated with coronary atherosclerosis.