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The room-temperature high energy ball-milling technique was used to prepare nanophase (x \ 0 ; Ce 1~x Zr x O 2 0.2 ; 0.5 ; 0.8 ; 1) catalysts. The acidÈbase properties of these catalysts were investigated by means of adsorption microcalorimetry, using and as probe molecules. The catalytic activity for 4-methylpentan-2-ol NH 3 CO 2 dehydration was tested at atmospheric pressure in a Ðxed-bed Ñow microreactor. The inclusion of increasingly high contents of zirconium into the ceria lattice has a complex inÑuence on the acidity and basicity of the pure parent oxide, in terms of both number and strength of the sites. A maximum in 1-alkene selectivity is observed for the ceria-rich catalyst and a minimum for the zirconia-rich sample. Catalytic results are correlated with the acidÈbase properties and can be interpreted in the light of the mechanism formerly proposed for zirconia, ceria and lanthania. Surface conditioning of the zirconia-rich catalyst occurs during the run, resulting in a remarkable variation of selectivity.