The apoptosis in bone tumor cells is studied after 153Sm-EDTMP irradiation.Fragmented DNA is analyzed by agarose gel electrophoresis.Experimental observations show that 153Sm-EDTMP exposureinduces the inteucleosomal DNA damage in bone tumor cells the DNAladder patte formation in bone tumor cells is shown.At the same time,the microautoradiographic study indicates that 153153Sm-EDTMP could permeate through cell membrane and displays membrane-seeking condensation in bone tumor cells.Soon afterwards 153Sm-EDTMP could be phagocytized by the tumor cells and distributed in cytoplasm as well as nucleus in the form of phagosome.With the prolongation of observing time, the membrane-bounded apoptotic bodies are observed.