To determine the patterns of gene expression responsible for the radiosensitivity of glioblastoma cells, we analyzed transcriptional changes after ionizing radiation in different cell lines. After completing clonogenic survival assays, we selected two glioblastoma cell lines with different radiosensitivities. Subsequently, they were investigated by using the technique of DNA microarray, and we then categorized the upregulated genes into 10 groups. Between the two cell lines, the difference in the percentage of DNA repair/replication category was the largest, and this category was present at a greater percentage with radioresistant cell line U87MG. Moreover, among the commonly upregulated genes, the DNA repair/replication category was present in the largest percentage. These genes included G22P1 (Ku70) and XRCC5 (Ku80) genes known as important members of the nonhomologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair. Furthermore, cell line that specifically upregulated genes included the members of major pathways of DNA DSB or single strand damage repair. These pathways were not only NHEJ, but also homologous recombination (HR) and postreplication repair (PRR). In conclusion, the distribution of genes involved in the DNA repair/replication category was most different between two human glioblastoma cell lines of different radiosensitivities. Among commonly upregulated genes, the DNA repair/replication category was present in the largest percentage.