A rare case of malignant fibrous histiocytoma of giant cell type originating in the lung of a 46-year-old woman is presented. The patient complained of having a cough that had lasted for a few weeks. A chest X-ray photograph showed a tumor shadow on the left lung. Histological and cytological examination of the biopsy specimen revealed that the tumor was a kind of sarcoma. An operative procedure was selected because of tumor invasion into the trunk of the left pulmonary artery, which was discovered on computed tomography examination, and because metastatic tumor was excluded clinically. The tumor was almost encapsulated and 6 × 6 × 6 cm in size; however, it also showed invasion into the pulmonary artery and bronchial lumen. A histological survey of the tumor showed a wide range of patterns such as fibrous, pleomorphic, fascicular and osteoclast-like giant cell figures; however, the osteoclast-like giant cell area was predominant. Immunohistochemically, the tumor cells were positive for vimentin, CD68 for histiocytic marker and α1-antichymotrypsin, and negative for keratin, epithelial membrane antigen, S-100 protein, MT-1, desmin, myoglobin and lysosome. No primary tumor was found clinically in any part of the patient's body at 2 and 4 months after operation. Consequently, she was diagnosed as having primary giant cell malignant fibrous histiocytoma of the lung.