The conductivities of a protonic conductor, 10 mole percent (m/o) In2O3-doped CaZrO3, were measured in an atmosphere containing hydrogen or deuterium with the 4-wires ac impedance technique at temperatures ranging from 623 to 1673 K. In high oxygen activities, H+/D+-isotope effects were observed below about 1100 K. The ratio of conductivities of protons to deuterons increased as the temperature decreased and rose to about 1.6 at 673 K. It was made clear by this observation that at low temperatures electrical conduction is dominated by proton and at high temperatures by positive hole, respectively. On the other hand, at high hydrogen activities, the isotope effects were observed up to about 1600 K and it was concluded that proton is dominant below this temperature. Over that temperature, the isotope effects vanished and the electrical conductivities were independent of gas potentials. It was concluded that electrical conduction over 1600 K was dominated by oxide ions. As electrical carriers obey the thermally activated process, the activation energies were calculated by the least squares method. The obtained activation energies of protons, deuterons, positive holes, and oxide ion vacancies were 0.74 +/- 0.05, 0.70 +/- 0.05, 1.21 +/- 0.07, and 2.5 +/- 0.5 eV, respectively. Based on the model of defects equilibria and these experimental findings, the protonic conduction domain of the specimen was determined and is represented in temperature-potential diagrams.