The structure, phase stability, and electrical properties of BaCe1-xYxO3-delta (x = 0-0.4) in humidity air and CO2 atmosphere are investigated. XRD results indicate that the BaCe0.9Y0.1O3-delta sample has asymmetric cubic structure, and its phase changes to tetragonal as the Y3+ doping amount increases to 20 mol%. The conductivity of BaCe1-xYxO3-delta increases with temperature, and it depends on the amount of yttrium doping and the atmosphere. BaCe0.8Y0.2O3-delta exhibits the highest conductivity of 0.026 S cm(-1) at 750 degrees C. The activation energy for conductivity depends on yttrium doping amount and temperature. The conductivity of BaCe0.8Y0.2O3-delta is 0.025 S cm(-1) in CO2 atmosphere at 750 degrees C which is 3.8% lower than that in air due to reactions with CO2 and BaCO3 and the CeO2 impure phases formed. The structure of BaCe0.8Y0.2O3-delta is unstable in water and decomposes to Ba(OH)(2) and CeO2 phases. It is found that the activation energy of samples in CO2 atmosphere is higher than that of sample in air. Sr-doped Ba1-ySryCe0.8Y0.2O3-delta (y = 0-0.2) is prepared to improve the phase stability of BaCe0.8Y0.2O3-delta in water. The conductivity of Ba0.9Sr0.1Ce0.8Y0.2O3-delta is 0.023 S cm(-1) at 750 degrees C which was 11% lower than that of BaCe0.8Y0.2O3-delta, however, the phase stability of Ba0.9Sr0.1Ce0.8Y0.2O3-delta is much better than that of BaCe0.8Y0.2O3-delta in water. (C) 2009 Elsevier B.V. All rights reserved.