Cell apoptosis in human acute lymphoblastic cell line Molt-4 and macrophage cell line Ana1 was induced by ,235,U. The cumulative radiation absorption doses of ,235,U in cultured cells through different periods were estimated. The morphological changes in Molt-4 and Ana-1 cells were observed by fluorescence microscopy. We found that Molt-4 and Ana-1 cells,internally irradiated by ,235,U,displayed a significant nuclear fragmentation and a marked pyknosis. The microautoradiographic study showed that at first ,235,U was phagocytized by Molt-4 and Ana-1 cells,and then ,235,U was homogeneously distributed through the cells. The finding indicated that ,235,U can significantly increase the DNA fragmentation and apoptotic bodies formation in the immune cells, and this effect could be inhibited by IL-2 and IL-6. So both IL-2 and IL-6 showed radioprotective effect on Molt-4 and Ana-1 cells internally irradiated by ,235,U.