A case of unclassified, pediatric cerebral neuroepithelial tumor in a 10-year-old girl that showed remarkable radiosensitivity is reported. MRI revealed a brain tumor of mixed intensity with heterogeneous enhancement in the medial temporal lobe, extending to the basal ganglia. The tumor was partially removed. On pathology, the main part of the tumor showed immature features: the tumor cells had a chromatin-rich large nucleus and less cytoplasm, and mitoses and fragmentation of the nuclei were frequent. On immunohistochemistry, the tumor cells were negative for glial fibrillary acidic protein (GFAP) and synaptophysin and positive for Olig2. The maximum MIB-1 index was 70%. The part invading into the surrounding brain showed similarities in form to a highly anaplastic astrocytoma. The infiltrating tumor cells were positive for GFAP and less positive for Olig2. After 40 Gy radiation, the residual tumor was markedly reduced. Neuroepithelial tumors rarely show such high radiosensitivity, and the reason for the radiosensitivity in the present case may have been the immaturity of the tumor cells.