Propylthiouracil(PTU) is a commonly used antithyroid drug in the management of hyperthyroidism. However, it is associated with a variety of side effects. Antineutrophil cytoplasmic antibody( ANCA)-positive vasculitis is an extremely rare side effect of PTU. We report a case of a patient with diffuse pulmonary hemorrhage while being treated with PTU. A 28-year-old woman was admitted due to fever and abdominal pain. She was diagnosed as Graves' disease 4 years before the admission, and was taking PTU intermittently. Thyroid storm was suspected and we treated her with PTU, hydrocortisone, lugol solution and propranolol. However, coughing was aggravated, with chest X-ray and computed tomography revealing diffuse alveolar hemorrhage. Perinuclear-ANCA was positive. After discontinuation of PTU, all symptoms resolved. In conclusion, ANCA-positive diffuse alveolar hemorrhage is a rare but a potential side-effect of PTU. Therefore, early awareness of this complication is important.