A deuterium-tritium (DT) neutron generator in Osaka University with a continuous intense neutron source emitting 3 × 10 12 fusion neutrons per second has been in operation since 1981. However, radioactivation for the parts of the accelerator body is a serious issue. Hence, in this study, we investigated the radioactivation of the intense irradiation room containing the continuous intense neutron source. Core samples of the concrete wall were collected at various positions in the irradiation room and the radionuclides in them were determined by performing gamma-ray spectrometry. Major long-lived radionuclides found were 54 Mn, 60 Co, and 152 Eu. The radioactivity of 152 Eu may possibly be consistent with the result obtained using the simulation code. The radioactivities of 54 Mn and 60 Co were minimal compared with that of 152 Eu. The tritium amount in the core sample was measured employing a tritium sampling system and a liquid scintillation detector and was found to be considerably larger than the amount estimated using the simulation code. Tritium diffused from the titanium-tritium target was attached to the wall surface. However, most of it did not penetrate the concrete wall. These results reveal the radioactivity issue of fusion neutron generator facilities and are expected to aid in the maintenance of their operation.