The effect of various amounts of ZnO addition on the densification behavior, electrical conductivity and chemical stability of high temperature proton conductor Ba1.03Ce0.5Zr0.4Y0.1O3-delta synthesized through citrate-nitrate method was investigated. Small amount of ZnO could considerably promote the densification process and the grain growth of Ba1.03Ce0.5Zr0.4Y0.1O3-delta. Samples with 0.5 wt.% ZnO achieved a relative density of 95.6% at 1250 degrees C, great higher than that without ZnO addition (50.4%). Field emission scanning electron microscopy observation revealed that ZnO addition led to the segregation of Y2O3 from the matrix. Part of ZnO existed at the grain boundary, its role was to form a eutectic melt to promote the densification process. A small part of ZnO dissolved into the lattice, which should be mainly responsible for the increase of bulk conductivity of Ba1.03Ce0.5Zr0.4Y0.1O3-delta With increasing ZnO level. ZnO also enhanced the grain boundary conductivity and increased the stability of Ba1.03Ce0.5Zr0.4Y0.1O3-delta, especially against boiling water. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.