The electrical conductivities of Ca1-xZrO3-delta (0 <= x <= 0.10) ceramics were measured as a function of nonstoichiometry (x) and oxygen partial pressure (Po-2) using impedance spectroscopy between 700 degrees C and 1100 degrees C. The stoichiometric CaZrO3 was a mixed ionic and electronic (hole) conductor in a high Po-2 region. It was an ionic conductor in a low Po-2 region. The analysis of impedance spectra revealed that the contributions of the grain and the grain boundary to the total conductivity were nearly constant independent of Po-2 at 700 degrees C. In addition, the grain boundary mainly determined the electrical conductivity at 700 degrees C. When the Ca deficiency (x) increased up to 0.02, the electrical conductivity rapidly decreased with x due mostly to the decrease in the grain boundary conductivity. (c) 2007 Elsevier B.V. All rights reserved.