Properties of hydrated and nanocrystalline zirconia and products of their thermal and chemical modification have been investigated by means of impedance spectroscopy, ion-exchange potentiometric titration, electron probe X-ray spectral analysis and electron microscopy. Regardless of the degree of hydration, all samples exhibit surface charge transfer. It was shown that ion conductivity of the hydrated zirconia could be increased by thermal treatment by one order of magnitude or more. (C) 2003 Elsevier B.V. All rights reserved.