An unusual case of refractory pneumothorax secondary to lung cancer in a 69-year-old man patient with idiopathic pulmonary fibrosis (IPF) is described. High-pressure suction applied through chest tube did not resolve the large right pneumothorax. Acute exacerbation of IPF has also appeared. Respiratory state worsened acutely, and the patient died on the fifth hospital day. In the present case, the large right pneumothorax was initially thought to be associated with IPF because pneumothorax is common in patients with IPF. However, postmortem microscopic examination revealed that the refractory pneumothorax was secondary to perforation of the pleura due to a necrotic peripheral lung cancer.