The morphological changes observed by electron microscopy indicate that after internal irradiation with ^153Sm-ESTMP bone tumor cells displayed feature of apoptosis,such as margination of condensed chromatin,chromatin fragmentation.as well as the membranebouded apoptotic bodies formation.THe quantification analysis of fragmentation DNA for bone tumor cells induced by ^153Sm-EDTMP shows that the DNA fragmentation is enhanced with the prolongation of internally irradiated time.These characteristics suggest that ^153Sm-EDTMP internal irradiation could induce bone tumor cells to go9 to apoptosis.