We report a rare case of a congenital pericardial defect that was incidentally found at thoracoscopic left upper lobe resection in a patient with lung cancer. A 75-year-old man with a left upper lobe lung cancer was referred to our hospital. We performed thoracoscopic left upper lobectomy and incidentally found a pericardial defect intraoperatively. Careful lymph node dissection was necessary to avoid injury of phrenic nerve and pulmonary artery. Surgery for lung cancer was completed without pericardial repair. After surgery, no complications associated with the pericardial defect has not been encountered.