Dense, tetragonal single-phased and nanocrystalline zirconia ceramics containing 3 mol % R2O3 without impurities and with average grain sizes of 60 nm were prepared. Electrical properties were investigated by impedance spectroscopy as far as the ionic radius is increased from 0.098 to 0.109 nm, respectively, from Yb3+, Y3+, Gd3+, to Sm3+. Conductivity variations were attributed to an effect of R2O3 dopant. Segregation phenomenon was demonstrated by comparison of these electrical data with those of air quenched samples and was fully related to the dopant ionic radius size. The grain boundary resistance and the width of the space charge layer were consequently increased while the bulk resistance was not changing and was in the same order of magnitude compared to the microcrystalline zirconia. (C) 2004 The Electrochemical Society.