We herein report a 73-year-old Japanese woman with metastatic thymic carcinoma who developed diffuse alveolar hemorrhage (DAH) during irinotecan chemotherapy. She presented with a mild fever and exertional dyspnea after the second cycle of weekly irinotecan monotherapy. Chest images showed diffuse ground-glass opacities. The diagnosis of DAH was based on the findings of the bronchoalveolar lavage fluid, which was bloody and contained hemosiderin-laden macrophages. The discontinuation of irinotecan and introduction of oral prednisolone improved her symptoms and chest abnormal shadows. This is the first case of DAH caused by irinotecan.