Recently, great attention has been drawn to IgG4-related diseases such as autoimmune pancreatitis (AIP) sclerosing sialadenitis, retroperitoneum fibrosis, sclerosing cholangitis. IgG4-related diseases are characterized by high serum IgG4 concentrations, sclerosing inflammation with numerous IgG4-positive plasma cells, and steroid sensitivity irrespective of their organs of origin. In this report, we describe a case of nonspecific interstitial pneumonia, in which possible involvement of IgG4 was suggested. The patient was 59-year-old man, who was found to have bilateral interstitial pneumonia. Laboratory tests revealed that he had antinuclear antibody and a high serum IgG4 concentration. Pathological examination of the video-assisted thoracic surgery biopsy taken from the right lower lobe showed interstitial thickening associated with lymphoplasmacytic infiltration containing many IgG4-positive plasma cells. He was effectively treated by corticosteroid. The present case had many clinical and clinicopathologic similarities to systemic IgG4-related autoimmune disease. There have been no descriptions on isolated interstitial pneumonia with IgG4-positive plasma cell infiltration. This case suggested that IgG4-related disorders could also occur in the lung, and interstitial pneumonia may be a pulmonary manifestation of systemic IgG4-related autoimmune disease.