Therapeutic uses of the radioactive isotope can be devided in 3 groups, i.e. 1) Brachytherapy. 2) Multicurie teletherapy and 3) Internal use of naked radioisotope. By utilizing their radioactivity, radioisotopes can be well adapted as effective means to radiaton therapy. From the beginning of the 20th century, natural radioactive substances, like radium, have been widely used for the purpose of the treatment of cancer and other diseases, and have been giving pretty good effects. In the present case of artificial radioisotopes, their applicable fields are not the same with radium, but reach far out to such broader extents, and larger amounts with varieties almost unthinkable with radium. New fields were also cultivated for application of radioisotope directly into human body, and thereby to bring out desirable therapeutic effects.