EPR paramagnetic probe method with 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO) as a probe has been applied to study of electron-accepting properties of the surface of (Y, La-0.1)CexZr1-xO2-y (x = 0.1-0.7), Y0.1Pr0.3Zr0.6O2-y and Y0.1Pr0.15Ce0.15Zr0.7O2-y mixed oxides. Two types of acceptor sites-coordinatively unsaturated (cus) cations Zr4+ and Ce4+-have been revealed on the CeO2-ZrO2 surface after thermovacuum treatment (820 K). The relative amounts and "strength" of these centers were evaluated on the basis of EPR spectra analysis. An introduction of trivalent Y3+ or La3+ cations reduces the amount of electron-acceptor sites belonging to cerium cations, stabilizing ones as Ce3+. A formation of very strong electron-accepting sites (Pr4+ cus cations) able to form charge transfer complexes with adsorbed TEMPO on the surface of praseodymia-containing samples after thermovacuum treatment was found out. At the same time electron-accepting ability of Zr4+ cationic sites on Y0.1Pr0.3Zr0.6O2-y and Y0.1Pr0.15Ce0.15Zr0.7O2-y surfaces decreases in comparison with ceria-zirconia one. The generally used IR spectroscopy technique with CO as a probe molecule appeared to be considerably less informative for such systems characterization, due to their high catalytic activity to carbon monoxide. A formation of paramagnetic Zr3+ ions in ceria-zirconia mixed oxides has been investigated by EPR spectroscopy technique. The different states of this paramagnetic ion are realized in the complex oxides depending on Ce/Zr ratio. (C) 2002 Elsevier Science B.V. All rights reserved.