Deuterium-tritium fusion neutrons, peaked at 14.1 MeV, can activate the materials employed in a fusion reactor. The radioactivation characteristics and level of activation that occurs in a fusion reactor after shutdown depend on the elements that are activated, the neutron wall loading, the duration of the exposure, and the neutron flux spectrum present. The radioactivity resulting from potential elements considered in fusion reactor designs is discussed. The dominating radionuclides and the levels of activation resulting from exposure of these elements to the neutron flux spectrum in the first-wall region of a typical Li20 solid-breeder fusion reactor blanket are also given.