The authors analyzed preliminary outcome of 10 patients with mixed glioma(3 patients with low-grade oligoastrocytoma and 7 patients with anaplastic oligoastrocytoma) who underwent surgical resection and were treated or are in treatment with or without adjuvant therapy at our institute since May 1993. In the low-grade oligoastrocytoma group, gross total tumor resection was done in all three cases and postoperative radiation therapy was performed in 2 cases. In the anaplastic oligoastrocytoma group, all seven cases were divided as to the amount of tumor removal(gross total resection; 4 cases, subtotal resection; 1 case, partial resection; 2 cases) and clinical course and prognosis were analyzed as to performing postoperative radiation therapy with or without chemotherapy. In the low-grade oligoastrocytoma group, one patient who didn't undergo postoperative radiation therapy suffered from tumor recurrence that showed histopathologically malignant transformation. In the anaplastic oligoastrocytoma group, 2 patients who underwent subtotal tumor resection and partial tumor resection with postoperative radiation therapy showed tumor progression and histopathologically more malignant transformation. The authors propose that gross total tumor resection with postoperative radiation therapy in low-grade oligoastrocytoma and adding chemotherapy(especially with procarbazine, lomustine, vincristine; PCV regimen) in anaplastic oligoastrocytoma appear to be associated with more prolongation of patient's survival.