The radioactivities on the materials of JT-60U fusion device, which decommissioning is underway toward the upgraded superconducting tokamak machine, have been evaluated by calculation and measurements on the specimens of the structure materials and the components. In the induced activities on those materials, the highest activation on the material was stainless steel. The essential nuclide was ^<60>Co in the stainless steels. The stainless steel 316 of about 35 tons constitutes the base of interiorities as a first wall on the vacuum vessel in JT-60U. For the management of radioactive materials, the evaluation for the steels with the activated nuclides is important. The activated structure materials are kept in the controlled area in the JT-60facilities, according to the criteria for handling activated materials by the defined domestic government.