Glioblastoma is a malignant brain tumor that is difficult to completely cure by surgical treatment alone. However, resistance to anticancer drugs and radiation may be acquired during treatment. For instance, miRNAs involved in regulating the expression of genes inducing apoptosis and other specific genes have been proposed for use, in order to induce the apoptosis of radioresistant cancer cells. A172 glioblastoma cells, expressing wild-type p53 were irradiated to a total dose of up to 60 Gy allowing us to analyze the activities of apoptosis-related proteins. The miR-34a expression levels in cells after irradiation at 30 and 60 Gy were 0.17- and 18.7-times the BCL2 and caspase-9 expression levels, respectively. The high miR-34a expression level in the cells after irradiation at 60 Gy reduced the p53 expression level. This study suggests that apoptosis might be promoted by regulating the action of miRNAs, even in cells that have acquired radioresistance.