A 62-year-old female was diagnosed with idiopathic thrombocytopenic purpura in 2007. In January 2011, diaphenylsulfone (i.e., dapsone) was administered instead of prednisolone because she had experienced side effects as a result of prednisolone. After diaphenylsulfone administration, she presented with fever, eruptions, and dyspnea. She was admitted to our hospital because the dyspnea worsened with a continuous fever, although the eruptions disappeared spontaneously. The laboratory findings showed elevated liver enzyme levels and eosinophilia. A chest X-ray and chest CT showed consolidations and diffuse reticular opacities associated with a few ground-glass opacities. Because we suspected that she had eosinophilic pneumonia associated with diaphenylsulfone, this drug was withdrawn on admission. Bronchoalveolar lavage revealed marked eosinophilia, and a transbronchial lung biopsy gave findings that were consistent with eosinophilic pneumonia. High-dose intravenous methylprednisolone was administered daily for three days, followed by oral prednisone. The fever and dyspnea improved immediately after therapy, and the chest X-ray shadows gradually disappeared. Kosseifi et al. previously reported that the classic triad of dapsone hypersensitivity syndrome (DHS) consists of fever, eruptions, and internal organ involvement relevant to eosinophilic pneumonia. This is a rare case report of DHS with eosinophilic pneumonia that improved after the administration of systemic steroid pulse therapy in Japan.