We report a case of gliosarcoma with numerous giant cells resembling ganglion cells and having clear nucleoli. A 75-year woman was admitted to our hospital suffering from progressive left hemiparesis and ambulatory disturbance of one week's duration. CT and MRI studies showed ring enhancement on a clear margin mass in the right parieto-occipital lobe. The mass was totally removed macroscopically. Her left hemiparesis had improved and self walk came to be possible. But the tumor was regrowthed during next two months and she died for three months and a week. The gross and microscopic appearances of the tumors showed the double structure. The surface of the tumor was well enhanced and consisted of soft, gray, and easily bleeding tissue. The central core, however, was poorly enhanced and consisted of hard, yellow, non-bleeding tissue. Macroscopically, the central area included numerous giant ganglion-like cells which were negative for GFAP but positive for EMA in the cytoplasm. These giant cells had abundant collagen fibers and were surrounded by such fibers. Microscopic findings of the surrounding area included numerous spindle shaped cells which were positive for GFAP and vimentin. The origins of giant cells or tumor tissues have long been discussed, but no consensus has yet been obtained. Therefore, we speculated as to the origin in our patient based on immunohistochemical study and the findings of electronmicroscopy. We concluded, in sharp contrast to the old theory of one origin, epithelial tissue of a hamartomatous nature existed initially, followed by the growth of malignant tissue of a reactive astrocytic tumor with a sarcomatous component.