A Zr-Ce mixed oxide with ca. a 1:1 atomic ratio is prepared by a microemulsion method and studied by X-ray diffraction, transmission electron microscopy, and Raman, X-ray photoelectron (XPS) and electron paramagnetic resonance (EPR) spectroscopies. The results show-the formation of a high surface area material (S-BET = 96 m(2) g(-1)) constituted by homodispersed particles of a major pseudocubic phase t" (as shown by Raman); the stabilization of the latter phase, instead of the normally more stable tetragonal phase t', is probably due to the small crystallite size (ca.. 5 nm). XPS indicates a moderate degree of surface enrichment in cerium. An EPR study is carried out on the superoxide species formed on the material by O-2 adsorption after outgassing at temperatures up to T-v = 773 K; this shows that the reduced surface centers thermally formed on this mixed oxide are similar to those found on pure ceria but are generated more easily than on the latter, thus evidencing a surface redox reactivity higher than that of the CeO2 single oxide.