This work presents results of multitechnique (HRTEM, EDX, XRD, XPS, ICP, BET and EELS) studies on structure evolution of nanocrystalline ceria-based Ce1-xYbxO2-(x/2) mixed oxides with increasing Yb content. Nano-sized (similar to 5 nm) mixed oxides were prepared by precipitation in water-in-oil (W/O) microemulsion method. No phase separation or/and segregation were observed for studied samples after heating in oxygen up to 950 degrees C. Realistic models of the intermediate structures (defected F- and C-type) for mixed oxides and mechanism of CeO2 -> Ce1-xYbxO2-(x/2) -> Yb2O3 structural changes have been proposed and tested (HRTEM images and diffraction patterns simulation). Reducibility of Ce1-xYbxO2-(x/2) mixed oxides and its changes with increasing of Yb content was measured and correlated with the structure features. The highest reducibility of Ce ions was observed for Ce0.5Yb0.5O1.75, which has a structure intermediate between F and C-type, with maximum number of defects and the highest average strain. (C) 2012 Elsevier B.V. All rights reserved.