Great saphenous vein is a conduit commonly used for coronary artery bypass grafting. However, several complications could occur at leg wound site for vein harvesting. Here, we describe a huge sac of hematoma as an uncommon complication of saphenous vein harvest for coronary artery bypass grafting.A 62-year-old gentleman was readmitted with swelling at left thigh 30 days after coronary artery bypass grafting. Lower extremity computed tomography was suggestive of an oval and thick sac implying a hematoma or seroma. After using ultrasound scanning for the mass, an incision through the previous surgical wound showed a huge mass. Inspection after incision the mass revealed an old hematoma within the sac.Pathologic findings demonstrated chronic inflammation with the hematoma surrounded by a fibrotic sac. The patient’s postoperative course was uneventful without recurrence.Our experience suggests the possibility of a huge hematoma within a thick fibrotic sac at the previous vein harvest site for coronary artery bypass grafting.