We have theoretically investigated the dielectric properties of fluorite CeO2 as well as hexagonal and cubic Ce2O3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO2 are in good agreement with previous theoretical and experimental results. For Ce2O3, the hexagonal phase has a lattice dielectric constant comparable to that Of CeO2, whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO2. (c) 2005 Published by Elsevier B.V.