We describe two cases of intractable pneumothorax that were attributed to a bronchopleural fistula (BPF) after radiofrequency ablation of lung tumors. In both cases, radiofrequency ablation induced necrosis of the lung tissue between the pleural space and the bronchus. The bronchopleural fistula formed after sloughing of the necrotic tissue. Management of the bronchopleural fistula was quite challenging, requiring frequent treatments, including pleurodesis, endobronchial management, and/or surgical repair. In one of the patients, air leakage persisted despite these efforts, and the patient died of acute pneumonia 52 days after the procedure. Although it is rare, with an incidence of 0.6% (2/334) at our institution, intractable pneumothorax due to bronchopleural fistula should be recognized as a risk associated with radiofrequency ablation of lung tumors.