Dense CeO2 layers of 350 nm thickness, with columnar grains of size 25 nm, were RF-sputtered on silicon. 18O isotope exchange in the temperature range from 200 to 575 °C showed surface exchange at CeO2 as the rate-determining step, while diffusion through the polycrystalline thin layer was fast. The surface exchange coefficients controlled by surface or grain boundary processes were found to be ks = 2.7 × 10- 8 exp (frac(- 0.3 eV, k T)) cm s- 1 or kgb = 1 × 10- 9 exp (frac(- 0.3 eV, k T)) cm s- 1. Comparison with literature data on doped ceria revealed that surface exchange could be dominated by grain boundary processes. A lower limit for the diffusion coefficient was determined as 10- 15 cm2 s- 1 at 575 °C. © 2007 Elsevier B.V. All rights reserved.