Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds. Oxalic acid, aniline and a reactive dye were used as representative of organic pollutants. In the case of oxalic acid, an increase in the catalytic activity with the increase of the percentage of Ce(III) on the surface was observed. Both single and catalytic ozonation allowed the total removal of aniline after 30 min of reaction: the cerium oxide prepared by the precipitation method was the best catalyst for promoting the mineralization of aniline solutions. TOC removals close to 100% were obtained in all cases when cerium oxides were used as catalysts in the ozonation of the reactive dye tested. (C) 2011 Elsevier B.V. All rights reserved.