Systematic investigation of Y-doped BaZrO3 was performed in the point of the relationship between dopant concentration, microstructures, and grain boundary conductivity. As Y concentration increased, average grain diameter increased by 4 times. But the trend of grain boundary character was not changed. Random boundaries were predominant in all samples. Grain boundary conductivity increased by the three orders of magnitude and activation energy was reduced with increasing Y concentration from 5 mol% to 15 mol%. Secondary phase was not observed in the 5 mol% Y-doped BaZrO3. Those results confirmed that contributions of observed parameter to grain boundary conductivity were low. Hence, the contributions of space charge layer was probably high in the Y-doped BaZrO3. (c) 2007 Elsevier B.V. All rights reserved.