The influence of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and chemical stability under CO(2) atmosphere of proton conductors with a nominal composition of Ba(1 +/- x)Ce(0.4)Zr(0.4)Y(0.2)O(3-delta) (B(1 +/- x)ZCY4, 0 <= x <= 0.20) was systematically investigated. A complexing sol-gel process was applied to synthesize the B(1 +/- x)ZCY4 powders. The X-ray diffraction patterns of the well-calcined powders indicate that the specimens with 0 <= x <= 0.10 possessed a single-phase of orthorhombic perovskite-type oxides. Additionally, impurity phases of (Y,Ce)O(2-delta) existed in B(1-x)ZCY4, and BaCO(3) was found in B(1+x)ZCY4 with x = 0.15 and 0.20. After sintering at 1500 degrees C for 5 h, all B(1+x)ZCY4 samples became pure phased, whereas impurities still existed in samples with large Ba deficiencies. A study of the sintering behavior showed that the proper amount of Ba excess or deficiency facilitated electrolyte densification and that a large Ba nonstoichiometry hindered sintering. The electrical conductivities of B(1 +/- x)ZCY4 specimens with 0 <= x <= 0.05 were studied in the temperature range of 100-700 degrees C, and the results showed that the Ba nonstoichiometry influenced the electrical conductivity, especially with respect to grain boundary resistance. The chemical stability was also studied using temperature-programmed CO(2) desorption, and it was determined that the chemical stability was affected by the Ba content. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.