A 71-year-old man was referred to our hospital because of an intractable productive cough. Although he was treated for bronchial asthma, the symptom did not improve. Furthermore, since he developed progressive dyspnea and hypoxemia, he was admitted to our hospital. Marked eosinophilia in a blood test and sputum, poorly defined centrilobular nodules throughout the bilateral lung fields in a chest CT scan, and mixed ventilatory impairment in a spirometric test were revealed. Thoracoscopic lung biopsy and bronchoalveolar lavage were not conducted because of progressive respiratory failure. Therefore, we clinically diagnosed eosinophilic bronchiolitis, and immediately administered oral prednisolone (30 mg daily). His symptoms and examination findings rapidly improved. This case suggests that eosinophilic bronchiolitis should be taken into consideration for differential diagnoses of eosinophilic lung disease and obstructive lung disease, and marked eosinophilia in sputum may be one of the useful tools for diagnosis of this disease when invasive examinations are inadequate.