BaZr1-xYxO3-delta is a proton-conducting oxide that has both high ionic conductivity and good chemical stability, but disadvantageously has low sinterability. In this work, two co-dopant systems, BaZr0.9(Y1-xMx)0.1O(3-delta) (M=Ga, In), were studied with the aim of improving sinterability. In both systems, sinterability was markedly improved. Although the addition of Ga markedly decreased the conductivity of BaZr1-xYxO3-delta, the addition of In did not decrease the conductivity significantly. It was shown that BaZr0.9Y0.05In0.05O3-delta is a practically useful material with a good combination of conductivity and sinterability. (C) 2008 Elsevier B.V. All rights reserved.