Abstract: Objective To study effects of human bone marrow mesenchymal stem ceHs(hBM-MSC)from bone marrow pretreated with low dose radiation(LDR).Methods The ceils were the hBM-MSC.They were exposed to X rays at the dose of 50 mGy,75 mGy、100 mGy(dose rate 12.5 mGy/min).The growth curve,cell cycle and apoptosis of hBM-MSC treated by LDR were investigated.The content changes of stem cell factor(SCF),interleukin-6(IL-6),macrophage colony stimulating factor(M-CSF)secreted by hBM-MSC after treated by LDR were determined by enzyme linked immunosorbont assay method.Results The growth rates of hBM-MSC treated by LDR obviously increase from 72 h.The cell cycle and apoptosis were examined with FORTRAN Atomatic Checkout Systom.The results show that the G0/G1 stage cells decrease after exposure to LDR,the percent of G0/G1 stage cells of 75 mGy at 72 h is the lowest(30.86%).However,the S stage cells percentage gradually increase at 48 h and 72 h.The most one is 75 mGy group at 72 h,which reaches to 68.88%.The apoptosis percentages have increased tendency at 24 h and 48h in all dose groups,especially in 100 mGy at 24 h(25.99%),while have decreased tendency at 72 h and the most decreased group is the 50 mGy(6.8%),transient enhancement of apoptosis ha the early stage and soon being decreased.The contents of SCF have increased tendency at 24 h,48 h.As for IL-6,the contents in different dose groups at 24 h and 48 h have up-regulation.These groups,50 mGy at 24 h,48 h,75 mGy at 24 h,48 h,100 mGy at 24 h have statistical difference compared with their control groups respectively.The content of IL-6 has greatest enhancement at dose of50 mGy.The contents of M-SCF in all the groups at 24 h,48 h and 72 h except for the 50 mGy dose at 72 h have also been found increased.The greatest increased content occur in the 75 mGy dose group at 72 h.Conclusion This conclusion show that LDR has hormesis effect on hBM-MSC in cell growth,cell cycle and content of hematopoietic factors.