A 62-year-old man with myelodysplastic syndrome (MDS) presented to our hospital with a high fever. Although treatment with broad-spectrum antibiotics was initiated, his respiratory status worsened to the point that he required mechanical ventilation. However, he was successfully treated with a corticosteroid without immunosuppression. Sequential transbronchial lung biopsies revealed abundant fibrin exudate in the alveolar spaces, which was subsequently replaced by fibroblasts, showing that acute fibrinous and organizing pneumonia (AFOP) gradually changes into organizing pneumonia. Our case demonstrated both the efficacy of corticosteroid-monotherapy and the histological course of AFOP.