CeO 2 -ZrO 2 mixed oxides were synthesized by two mild chemical routes: complexation with citric acid and the sol-gel method. XRD and ESEM investigations revealed the appearance of a solid solution around 400 °C, depending on the ratio between the two oxides and the preparation method. Solids obtained by the citrate method were more homogeneous on the whole range of composition. Solid-state investigations of the prepared materials did not show segregation of cerium or zirconium oxides, except in the high Ce ranges for samples prepared by the sol-gel method. The thermal stability of both oxides was enhanced by mutual substitution. The most stable solid solutions were obtained in the range 50 < Ce < 90% mol.