The effects of cerium addition on the physico-chemical properties and CO oxidation activity of nanostructared MnCeOx catalysts (0 <= C-Ce <= 1) have been assessed. Irrespective of the loading, cerium hinders any significant long-range crystalline order promoting surface exposure, oxide dispersion, and reducibility of composite catalysts. Noticeable structural effects and strong oxide interaction lead to different arrangement of the active MnOx phase, explaining the peculiar reactivity scale of the studied catalysts in the CO oxidation reaction. High activity, good stability, CO2 productivity values depending on the MnOx loading, and similar activation energy values in the range of 353-533K (37-47 kj/mol) uncover an unchanging reaction mechanism, irrespective of composition and temperature. Although some chemical effects at high Ce loading (chi(Ce) >= 0.5), structure-activity relationships indicate that surface Mn-IV centers are the active sites of bulk MnOx and composite MnCeOx catalysts. (C) 2017 Elsevier B.V. All rights reserved.