The electrical conductivity in BaCe0.9Y0.1O3-delta Was measured as the functions of partial pressure of oxygen, P (O-2), water vapor partial pressure, P(H2O), and temperature. The electrical conductivity showed strong dependence on P(O-2) and temperature, while the dependence on P(H2O) Was weak. The defect structure and diffusivity of ionic defects and hole were discussed using electrical conductivity data and the defect chemical equilibriums obtained by the high-temperature gravimetry reported in Part 1. The obtained diffusivity of oxygen vacancy, proton and hole were compared with those of the various proton conducting perovskite-type oxides reported in the past literatures. The oxygen vacancy diffusion coefficients of BaCe0.9Y0.1O3-delta showed larger value compared to that of zirconate-based proton conducting perovskite-type oxides. Similar values of the proton diffusion coefficient were obtained for cerate and zirconate based proton conducting perovskite-type oxides. The proton diffusion coefficient was found larger than the oxygen vacancy diffusion coefficients. The activation energy of the proton diffusion coefficient was smaller compared to that of oxygen ion. The mobility of the hole was 2 to 3 order of magnitude larger than the diffusivity of the oxygen vacancy and proton. The weak P(H2O) dependence of the electrical conductivity was observed in BaCe0.9Y0.1O3-delta, while strong dependence on P(H2O) are reported in zirconate-based ceramics. The different P(H2O) dependence was interpreted by the large difference in the oxygen vacancy diffusion coefficients between cerate and zirconate based ceramics. (C) 2008 Elsevier B.V. All rights reserved.