Microarrays except for cDNA expression arrays was used to profile changes in gene expression of bone marrow cell after exposed BALB/c to ionizing radiation (IR). The RNA from bone marrow cells was subjected to cDNA analysis on a microarray of 8079 known genes and ESTs.Data analysis showed that 660 genes changed at least 2-fold.among the 660 genes, 354 genes showed up-regulation in the radiated BALB/c, whereas 306 genes were down-regulated. 222 of the 660 genes are function known or inferred genes, which fell into categories of signal transduction, immunity or defense response, nucleic acid correlated, apoptosis, cell cycle, transport, metabolism etc. It is suggested that a variety of regulatory pathways in hematopoietic cells were affected by irradiation.