The influence of a high temperature annealing (similar to 2200 degrees C) on the microstructure and the electrical properties of BaZr0.9Y0.1O3-delta has been examined. The high temperature annealing was achieved using an optical floating zone furnace. The obtained sample is homogeneous with an average grain size of about 5 mu m. No additional phases were found in the XRD pattern and the structure was identified to be cubic. After the high temperature annealing, the grain boundary conductivity is increased by approximately two orders of magnitude, while the bulk conductivity remains the same. (c) 2007 Elsevier B.V. All rights reserved.