AbstractA beryllium irradiation study with the Japan Materials Testing Reactor of JAERI is reviewed from the point of view of tritium release, thermal properties, mechanical properties and reprocessing technology by using the neutron irradiated sample with a total fast neutron fluence up to 1021 (n cm−2). It becomes clear that problems arise for each of the properties, for example, effects of the surface oxide layer, impurities, grain size, and/or swelling. Moreover, future plans of beryllium irradiation studies are discussed in this paper.