[RESULTS and DISCUSSION] First, isolated cells from BM cells were evaluated by flow cytometry and osteogenic differentiation. Isolated MSCs expressed CD105, not CD45. Irradiation suppressed MSCs proliferation in a dose-dependent manner. But, irradiation didn't alter the osteogenic differentiation ability in MSCs. Furthermore, mRNA expression levels of hematopoiesis-related cytokine such as Kitl, Thpo, Flt3l, Il6 and adhesion molecule such as Cxcl12, Vcam1 increased in irradiated MSCs. These results suggested that irradiated MSCs could promote engraftment and expansion of infused HSCs in HSCT.