The electrical properties of BaCe0.65Zr0.2Y0.15O3-delta (BCZY) were studied as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of 500-800 degrees C, and the partial conductivities of protons, holes, and oxygen vacancies were calculated from the defect model. P-type conduction was dominant in an oxidative atmosphere. In a wet atmosphere, BCZY was a mixed conductor of protons, holes, and oxygen ions. A conduction transition from protons to holes and/or oxygen ions was found with increasing temperature. The calculated activation energy of oxygen ion transport was 0.71 eV. The standard solution enthalpy for water dissolution was best fitted with a slope of -120.19 kJ/mol, which is somewhat smaller in absolute terms than that of BaCe0.9Y0.1O3-delta and of BaCe0.8Y0.2O3-delta. This result also agrees well with the literature reports that the Ba, rather than Sr, occupation of A-site and the Ce, rather than Zr, occupation of B-site in perovskite proton conductors induce more negative hydration enthalpies due to the increasing basicity of the corresponding oxides. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.