The chemical stability and electrical properties of three promising perovskite-related structures BaCe0.8Gd0.15Pr0.05O3-delta, BaCe0.85Sm0.15O3-delta, and BaCe0.85Eu0.15O3-delta were tested in air, humidified N-2 and H-2, as well as in D2O + N-2. Powder X-ray diffraction studies confirmed the formation of a cubic perovskite-like structure. The change in the lattice constant was consistent with B-site substitution in BaCeO3. All the investigated compounds formed barium carbonate in CO2 at elevated temperatures and were found to be chemically unstable in boiling H2O. The data showed that these three compounds are chemically stable in humidified CH4 at 800 degrees C; however, at 600 degrees C, the formation of barium carbonate was observed. The electrical conductivity in wet N-2 and/or H-2 was found to be higher than that in the D2O-containing atmosphere, confirming proton conduction in the doped BaCeO3. The Gd + Pr co-doped BaCeO3 showed the highest total conductivity of 2.58 x 10(-2) S cm(-1) in H-2 + 3% H2O at 700 C with an activation energy of 0.36 eV in the temperature range of 450-700 degrees C. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3464774] All rights reserved.