We report a case of iatrogenic diaphragmatic hernia following partial resection of the left lung via thoracoscopic surgery. A female in her 60s underwent partial resection of the left lung via thoracoscopic surgery on suspicion of primary lung cancer. The pathological finding was granuloma. Four months after surgery, she experienced pyrosis, and her radiograph showed a gastric bubble in the left thorax. Coronary-section computed tomography demonstrated that the gastric fundus had pushed into the left thorax. We performed elective video-assisted thoracic surgery because she did not show any symptoms. After the adhesiolysis, the herniated stomach was returned into the abdominal cavity, and the hernial orifice of the diaphragm was directly sutured. The postoperative course was uneventful, and the patient was discharged on the 12th postoperative day and is doing well. We should consider the possibility of iatrogenic diaphragmatic hernia following thoracic surgery during which an invasive technique involving the diaphragm was undertaken.