Ionising radiation (IR) causes DNA (deoxyribonucleic acid) injury and activates intracellular signal pathways including the regulation of DNA repair and cell cycle. However, the further knowledge of molecular events involved in radiation exposure is essential to more comprehensively understand the effects of irradiation. Therefore, the gene expressions of mRNA (messenger ribonucleic acid) by X-ray irradiation in human B lymphoblast cell line (IM-9) using a microarray were investigated. The mRNA expressions of 65 genes were shown to be up-regulated at >2.0-fold in irradiated cells (4 Gy) when compared with non-irradiated cells (0 Gy) by microarray analysis. Among 65 genes, a large number of genes were up-regulated with an X-ray dose-dependent change. These results indicate that the up-regulation of their mRNAs is the effects of irradiation and may be due to biological dosimetric markers for the evaluation of radiation exposure in the future.