It is known that low dose ionizing radiation stimulated the immune functions in human subjects and mice. In order to examine the situation of macrophages a series of changes in the immune system in Kunming mice following low dose whole body irradiation were observed based on the study of macrophages from spleen. The present study was designed by whole body X-rays with the doses of 50, 75, 100 and 250 mGy, respectively, The dose rate was 12.5 mGy/min. All the results showed that low dose irradiation may enhance the function of macrophages on the reaction of lymphocytes to ConA, and increase content of IL-1 from macrophages.