Abstract: Paraneoplastic pemphigus (PNP) is a rare and life-threatening autoimmune blistering disease characterized by severe mucosal erosions and polymorphous cutaneous eruptions associated with lymphoproliferative neoplasmas. Castleman's disease, non-Hodgkin's lymphoma, thymoma, follicular dendritic cell sarcoma and chronic lymphocytic leukemia are the commonly associated neoplasmas in PNP, whereas malignant thymoma is rare. The prognosis of PNP is poor due to severe infections during immunosuppressive treatment, underlying malignancies and bronchiolitis obliterans mediated by autoimmunity. A 58-year-old woman who experienced recurrent oral erosive ulcer for 3 years, systemic erythema for 10 months, and dyspnea for 3 months was diagnosed with PNP with malignant thymoma and obliterated bronchiolitis by clinical, radiological, histopathological, and immunological examinations. She died of respiratory failure 3 weeks after resection of the malignant thymoma.