A 61-year-old man with acute myocardial infarction underwent percutaneous coronary intervention with stent for the left main coronary artery (LMT) and the left anterior descending artery (LAD). Three months later, we recognized the LMT aneurysm complicated with possible thrombus formation, which developed in size during 6 months. In addition, the LAD stent showed significant in-stent stenosis. For the purpose of supplying blood flow to the distal of LAD, and avoiding myocardial infarction due to distal thrombosis possibly originated from LMT aneurysm, we decided to perform surgical operation. On preoperative examination, this patient had an obstruction of the right internal carotid artery. Although the direct repair of LMT aneurysm requires conventional approach with cardiopulmonary bypass, we applied off-pump coronary artery bypass grafting( OPCAB) considering the risk of cerebrovascular event. Consequently, OPCAB was performed in usual fashion [right internal thoracic artery (RITA) -LAD, left internal thoracic artery-left circumflex artery (LITA-LCX)] followed by the ligation of the proximal of LAD and LCX without cardiopulmonary bypass. The patient had a good operative course.