We report a case of IgG4-related inflammatory pseudotumor of lung, which coexisted with autoimmune pancreatitis. A 65-year-old man was admitted with left lung mass and left upper abdominal pain. A biopsy was performed for the lung mass under suspicion of malignancy. Microscopic examination demonstrated the proliferation of spindle cells, fibrosis and heavy infiltration of plasma cells, which were strongly immunoreactive for IgG4. Diffusely enlarged pancreas in abdominal computed tomography scan and elevated serum IgG4 level suggested the patient also had an autoimmune pancreatitis. We concluded this patient had the pulmonary inflammatory pseudotumor, as well as the autoimmune pancreatitis. These features were manifestations of the so-called IgG4-related sclerosing disease, which is a recently proposed clinicopathological entity, characterized by extensive IgG4-positive plasma cell infiltration and sclerosing inflammation in various organs.