The authors report a case of frontal gliosarcoma. The characteristic of this tumor is that it is composed of mixed glial and sarcomatous elements. The sarcomatous elements are thought to derive from the neoplastic transformation of mesenchymal cells in or adjacent to the tumor. This transformation usually has the appearance of a fibrosarcoma or angiosarcoma. A 24-year-old man had a 1-month history of headache, dizziness followed by blurred vision. At admission, there was no focal neurological deficit except bilateral papilledema. Brain CT and MRI revealed a heterogeneously enhancing mass containing cystic portion in the right frontal lobe with considerable peritumoral edema and shift of the midline structures. A craniotomy was performed with gross total resection of the tumor. Postoperative course was uneventful with resolution of his symptoms. The histologic, immunohistochemical and electron microscopy studies revealed bimorphic pattern, a characteristic feature of gliosarcoma.