Dense sintered bodies of the 15-25 mol% Yb-doped BaZrO3 could be obtained at a fairly low sintering temperature of 1500 degrees C, by the addition of 1.0 mol% CuO as a sintering aid. The crystal structures changed from orthorhombic (space group: Cmm2) to cubic (space group: Pm3m) by the CuO addition. The proton conductivity of thus-obtained 20 mol%Yb-doped BaZrO3 with the 1.0 mol% of CuO addition was 55 x 10(-3)S/cm at 600 degrees C under the wet nitrogen atmosphere, which was comparable to that of the 15 mol% Yb-doped BaZrO3 sintered at 1700 degrees C for 20 h without the CuO addition. (C) 2009 Elsevier B.V. All rights reserved.