We report a rare case of gastropleural fistula as a result of diffuse large B-cell lymphoma of the stomach. A 67-year-old male with rheumatoid arthritis was admitted to the hospital because of left chest pain and fever. Chest radiography and CT showed left pneumothorax and multiple air-fluid levels in the left pleural cavity. Although pyopneumothorax was suspected, the fluid in the pleural cavity was rapidly decreased before insertion of the chest drain. The left lung expanded easily after the chest tube insertion, and Candida species were cultured from the pleural effusion. Gastrointestinal endoscopy revealed that the cause of left pyopneumothorax was diffuse large B-cell lymphoma of the stomach that perforated to the left pleural cavity. We must be aware that gastropleural fistura is one of the causes of pyothorax, and isolation of Candida species from pleural fluid is an important clue for suspecting gastrointestinal tract perforation as a cause of empyema.