The aim of this study was to investigate the effect of radiation on the expression of interleukin — 6 in the bone marrow stromal cells (BMSCs) and to discuss the mechanisms by which the expression of interleukin — 6 increased. The BMSCs from normal Kungming mice were cultured in vitro with the method of Dexter. The expression of interleukin — 6 on the levels of protein and mRNA were detected by the uses of radio—immunity assay(RIA) and the reverse transcription polymerase chain reaction(RT—PCR) respectively. PDTC and dexamethasone, two different inhibitors of nuclear factor—kappa B, were used as controls. The result of RIA showed that the expression of interleukin—6 were distinctly increased at 1 hour, with its peak at 4 hours post irradiation in the supernatant of culture of murine BMSCs when the BMSCs were irradiated by 8.0 Gy ,60,Co ,γ, rays. The results of RT—PCR showed that the expression of IL—6 mRNA reached its peak at 8 hours. After adding NF—kappa B inhibitor in the supernatant before radiation, there was no difference between control group and radiation group in detecting the mRNA of IL — 6 using RT—PCR. This study suggested that the transcription and expression of IL—6 were activated by ionizing radiation, which might be due to the reason that ionizing radiation could activate NF—kappa B.