We report a case of localized malignant mesothelioma. The patient was a 37-year-old male, admitted to our hospital because of a solitary nodular shadow in the right middle lung field noted on chest X-ray. Five years prior to admission, a solitary nodular shadow had been seen in the same area on chest X-ray, and the diameter of the tumor had gradually increased. A transbronchial biopsy specimen revealed proliferation of spindle-shaped tumor cells, suggesting fibrosarcoma. No other lesions were identified as primary foci, so we made the tentative diagnosis of primary pulmonary sarcoma prior performing right upper lobectomy. The resected specimen revealed that the tumor, which partially touched the pleura, contained a number of large and small cystic spaces, and was composed of numerous spindle-shaped tumor cells. Some of the tumor cells were immunohistochemically positive for cytokeratin and epithelial membrane antigen, and many mitotic figures were noted. Thus, we made the histopathological diagnosis of localized malignant mesothelioma.