A 20-year-old man who had no previous history was seen at our emergency clinic because of the sudden onset of left chest pain at rest. A chest x-ray showed mild left pulmonary collapse and pneumopericardium. A chest CT scan showed left pneumothorax, pneumopericardium, and a partial defect of the left pericardium at the left hilus of the lung. The diagnosis of left partial defect of the pericardium and left spontaneous pneumothorax was made and thoracoscopic-assisted operation was performed. Intraoperatively, a 4×3cm partial defect and bullae were noted. Bullae were resected without performing any treatment such as repair for the pericardial defect. The postoperative course was uneventful and the patient was discharged seven days after the operation. In the treatment of pneumothorax associated with pneumopericardium, congenital pericardial defect must be kept in mind as a differential diagnosis, though it is rare. Some treatments including repair are required in a patient at a high risk of developing cardiac hernia, but observation of the clinical course can be the treatment of choice according to the degree of symptoms or the size of the defect.