A 70-year-old man presented with progressive dyspnoea and weight loss. Physical examination revealed only mild pale conjunctiva. The workup showed mild anaemia, mild impaired renal function, and high globulin level. Multiple myeloma was excluded by normal serum protein electrophoresis. The chest radiography and computed tomography (CT) revealed bilateral multifocal patchy infiltration with mediastinal adenopathy. Bronchoscopy was performed. Bronchoalveolar lavage (BAL) fluid examination was negative for infection and malignancy. Tissue pathology revealed diffuse lymphoplasmacytic cell infiltration. Immunohistochemistry revealed positive highlight for CD38, immunoglobulin G (IgG), and IgG4. Serum IgG subclass was requested and showed an IgG4 level of 7230 mg/dL. Examination of bone marrow and submental lymph node pathology were also positive for IgG4. IgG4-related disease with pulmonary involvement was diagnosed. Treatment with prednisolone (30 mg/day) resulted in improvement in his dyspnoea and almost complete resolution of the pulmonary infiltration on repeated CT at 6 month. This case highlighted a rare occurrence of IgG4-related disease which was successfully treated with steroid.