Abstract Effects of hydrogen (proton) in the electrical conductivity of ceramics were studied, with protonic conductive perovskite-oxides. Large electrical conductivity was observed at elevated temperatures under fission reactor irradiation, which could be explained by the contribution of protonic conduction. At elevated temperatures, existence of high concentration hydrogen (proton) will increase the ionic conductivity. Reduction of ions constituting the oxides was observed in electron irradiation as well as 14 MeV neutron irradiation at room temperature, which will result in radiation induced phase changes. The results imply that role of hydrogen in radiation effects in oxide ceramics is important, which may evoke technological problems in fusion machines.