We report a case of an anomalous origin of the left coronary artery from the right aortic sinus in young boy with exertional syncope. A 15-year-old boy was admitted to the hospital because of severe retrosternal chest pain followed by syncope during exertion. He had a similar history of syncope during exercise previously. On site transthoracic echocardiography showed that abnormal color mosaics course between aorta and pulmonary artery, suggesting the anomalous left coronary artery originated from the right aortic sinus, and the definite diagnosis was made by multidetector computed tomography (MDCT) thereafter. Coronary angiography showed anomalous origin of the left main coronary artery (LMCA) from the right coronary sinus. The right coronary artery was normal. Mid portion of the LMCA was angulated and narrowed significantly. Surgical correction of the left coronary artery by reimplantation of the ostium to the left aortic sinus and augmentation of the ostium using oval vein patch was performed successfully.