Radiation therapy is sometimes performed to control intracranial acute lymphoblastic leukemia (ALL), but may lead to radiation-induced malignant glioma. The clinical, radiological, histological, and molecular findings are described of three cases of radiation-induced glioblastoma after the treatment for ALL. They received radiation therapy at age 6–8 years. The latency from radiation therapy to the onset of radiation-induced glioblastoma was 5–10 years. Magnetic resonance imaging demonstrated diffuse lesions with multiple small enhanced lesions in all cases. Histological examination showed that the tumors consisted of mainly small round astrocytic atypical cells in one case, and astrocytic atypical cells with elongated cytoplasm and nuclear pleomorphism with small cell component in two cases. Microvascular proliferation was present in all cases. Immunohistochemical analysis for B-Raf V600E, and mutational analysis for the isocitrate dehydrogenase (IDH) 1, IDH2, and H3F3A gene revealed the wild-type alleles in all three cases. The integrated diagnoses were IDH wild-type glioblastoma, and local irradiation and concomitant temozolomide were performed. After the initial treatment, significant shrinkage of the diffuse lesion and enhanced lesion was found in all cases. Radiation-induced glioblastoma occurring after the treatment for ALL had unique clinical, radiological, histological, and molecular characteristics in our three cases.