This is a case report of a 60-year-old woman with acute myocardial infarction (AMI) who had coronary aneurysms and thrombus in the right coronary artery detected by multi-detector row computed tomography (MDCT). In this case, MDCT was useful for clarifying the thrombus complicated with coronary aneurysms, which was considered to be the cause of AMI. Thus, warfarin was started as an anticoagulant therapy for thrombus.