To elucidate the possible mechanism of immunoenhancement after low dose radiation (LDR) . The regular of changes of IL-2Rα expression in splenocyte following low dose irradiation was studied. IL-2R expression was induced by Con A in vitro 24 hours after whole-body irradiation (WBI) . The expression of IL-2R in splenocyte was analyzed by direct immunofluorescence flow cytometry. It was found that the expression of IL-2R in splenocyte was shown significantly increased (p ,<,0.05) 24 hours after WBI with doses of 50~500mGy, in which the percentage of CD25 positive cells was significant higher than that in sham irradiated group, and the highest was in irradiated group with 50mGy (,p,<,0.01) . The percentage of CD25 positive cells did not change significantly after WBI with 1.0~2.0Gy (,p,>,0.05) . However, the percentage of CD25 positive cells decreased significantly after WBI with 4.0~6.0Gy (,p,<,0.05,p,<,0.01 respectively) . The results indicate that LDR might enhance and stimulate the expression of IL-2R in splenocyte. The results are important to elucidate the mechanism of immunoenhancement after low dose radiation. The results following WBI with higher doses suggested that WBI with higher doses might suppress the expression of IL-2R in splenocytes.