Metastatic lung tumor was suspected in a 52-year-old woman who showed multiple nodules on her chest radiographs. Conventional examinations did not define the diagnosis, and so a biopsy was performed using video-assisted thoracoscopic surgery. Pathological examination demonstrated deposits of amorphous materials which were stained red by Congo red staining, even after potassium permanganate treatment. Green birefringence was also observed in the deposits under a polarized light microscope. A diagnosis of localized pulmonary amyloidosis with AL type amyloid protein was made, and therapy with dimethyl sulfoxide (10 ml/day) was started. During the two-year therapy, little exacerbation on pulmonary nodules was observed. It was suggested that dimethyl sulfoxide inhibited the progression of the disease.