Gliosarcoma is a rare tumor of the central nervous system characterized by a biphasic histological pattern. Our objective is to describe clinical, morphological and immunohistochemical features of two cases of gliosarcoma with chondroblastic osteosarcomatous differentiation and to discuss its pathogenetic mechanisms. Case 1: A52- year-old male patient underwent parietal craniotomy due to anaplastic ependymoma. The case had radiotherapy and chemotherapy postoperatively. After the first operation, additional resections were performed for tumor because of recurrences at the fourth, seventh and tenth months. The patient died after the last tumor resection. Histopathologic examination of the postmortem biopsy revealed neoplasm displaying a biphasic morphologic pattern including both gliomatous and sarcomatous components. Case 2: The case was a 69-year-old male patient with a right frontal lobe mass histologically diagnosed as gliosarcoma displaying sarcomatous and glial components. Immunohistochemical features were similar to those of the first case in general, but diffuse nuclear reaction with p53 protein was detected in both components. We report two cases with an extremely rare histopathologic aldiagnosis of “gliosarcoma with features of chondroblastic osteosarcoma”.