Nanostructured cerium dioxide rods and powders were synthesized via two sol-gel routes, respectively at 200 degrees C, and in room conditions without any thermal treatment. The initial solution involved nitrates, urea and polyvinyl-pyrrolidine in aqueous medium. In a first step, we synthesized cerium oxycarbonate by heating the solution at 80 degrees C: crystalline grains of (Ce3+)(2)O(CO3)(2), H2O phase were obtained in the form of elongated crystalline spindles (5-10 mu m long). Thermal decomposition of these spindle-like crystals gave rise to smaller elongated rods of nanostructured ceria. A second sol-gel route allowed obtaining nanosized ceria, after NH4OH addition and without any heating process. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses allowed characterizing the oxycarbonate polycrystalline samples and the two types of nanocrystalline ceria phases. (c) 2008 Elsevier B.V. All rights reserved.