In the present work, a set of Ce-Zr-O catalysts was prepared to study the effect of Zr-content (in the range 10-30 at.%) and the surface-dependency activity towards CO oxidation, a prototypical reaction for oxidation catalysis. The physico-chemical features of the prepared materials were investigated using complementary techniques. As a whole, it was observed that the oxidation activity of ceria-zirconia nanocatalysts mainly depends on the presence of (100) and (110) crystalline planes, thus confirming the structure-sensitivity for this reaction over Ce-Zr mixed oxides. Moreover, the abundant population of carbonate-like species on more open and reactive surfaces has a beneficial effect on the reactivity of the Ce-Zr-O nanomaterials. The best compromise between the structural defects and redox-active centres (Ce3+/Ce4+ pairs) was observed for the most active nanocatalyst, namely the Ce0.9Zr0.1O2-NP (nanopolyhedra with sizes of about 20-40 nm). The latter exhibited better CO conversion values compared to similar Ce-Zr-O nanocatalysts with higher Zr-contents (namely, Ce0.8Zr0.2O2-NP and Ce0.7Zr0.3O2-NP). On the other hand, lower activities were obtained for the high-surface-area catalysts (e.g. mesostructured materials) with the same Ce/Zr ratio, thus showing the key role played by the structural features of solid catalysts for this reaction. (C) 2016 Elsevier B.V. All rights reserved.