A 62-year-old woman had been treated with propylthiouracil(PTU) for hyperthyroidism. Because bloody sputum, dyspnea, and severe hypoxemia developed, the patient was admitted to our hospital. Chest X-ray and chest computed tomographic (CT) films disclosed diffuse infiltrative shadows in both lung fields. Bronchoalveolar lavage revealed abundant hemosiderin-laden macrophages. Alveolar hemorrhage associated with myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) positive vasculitis syndrome was diagnosed because of the high serum level of MPO-ANCA. After the initiation of steroid therapy and termination of PTU, the infiltrative shadows in both lung fields disappeared, PaO2 improved, and MPO-ANCA decreased. There have been some reports of MPO-ANCA positive vasculitis syndrome developing during PTU therapy, but most were concerned with renal disease. We concluded that PTU and similar agents should be given consideration as one of the possible causes of MPO-ANCA-induced alveolar hemorrhage.