The IgG4 related sclerosing disease is defined as a dense IgG4+ lymphoplasmocytic tumefactive fibroinflammation and aller-gic disease (atopy, eczema, asthma, modest peripheral eosinophilia) which involves virtually any systemic organs in human being. This disease may be contributed by half antibody exchange reaction/fragment antigen-binding (Fab)-arm exchange reaction. It is composed of serum IgG4+ increase, IgG4+ plasma cells, storiform fibrosis and inflammatory pseudotumor and modified Th2 response (IL-4, -13; IL-10, -12, -21). This disease is also known to be related with subsequent neoplasm. A fifty year-old woman complained of acute onset of fever, cough and sputum. The radiologic findings showed total consolidation in the right lower lobe. This lesion was not slowly responsive to antibiotics. The pathologic findings were lymphocytic infiltra-tion, which were stained positively with IgG4. After steroid therapy, this lesion became markedly resoluted but further fol-low-up would be mandatory.