A 70-year-old Japanese man with mantle cell lymphoma underwent extensive chemotherapy and radiation because of the relapse of mantle cell lymphoma. He developed mediastinal emphysema and a pneumothorax 14 days after treatment with 560 mg of ibrutinib. The mediastinal emphysema and the right pneumothorax disappeared after the ibrutinib treatment was tapered off. The patient developed interstitial pneumonia without any infection and new lesions of mantle cell lymphoma in the lungs after restarting treatment with 560 mg of ibrutinib. In this case, the patient developed pneumonia after retreatment with ibrutinib, suggesting the small lung fibrosis that penetrated the mediastinum might have caused the emphysema and pneumothorax.