A mixed conductor, ZrO2-CeO2-Y2O3 (Ce-YSZ), exhibits anomalous electrical properties depending on oxygen partial pressure and CeO2 concentration. We measured surface reaction rates and oxygen tracer diffusion coefficients of YSZ with various CeO2 concentrations by secondary ion mass analyses. The Ce concentration dependence of oxygen tracer diffusion coefficient in air corresponds with that of the total electrical conductivity, over which the ionic conductivity is dominant. The surface exchange coefficient, however, had a higher value in the region of 20 similar to 60 mol% CeO2 containing YSZ compared to other compositions. Ce-YSZ, which contains this region of CeO2 concentration, exhibits high electronic conduction at reducing conditions. The ionic and electronic conductivities are considered to affect the oxygen tracer diffusion coefficient and the surface exchange coefficient, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.