A 71-year-old man with a history of rheumatoid arthritis was treated with intravesical bacillus Calmette-Guérin (BCG) instillation of 80 mg once-a-week for carcinoma in situ. He developed low-grade fever followed by dyspnea and severe hypoxemia. Radiological and laboratory studies revealed bilateral diffuse reticulonodular infiltrates and hypereosinophilia. A lymphocyte stimulation test for BCG was strongly positive. From these findings, a pulmonary hypersensitivity reaction to immunotherapy was suspected, and therefore, methylprednisolone (500 mg per day) was started. After that, the fever and dyspnea disappeared, the hypereosinophilia was normalised and chest radiography results were clear. The present case is the first reported case of eosinophilic pneumonia following intravesical BCG therapy.