Two commercial high BET surface areas CeO2 are characterized, as received and after calcination at different temperatures, to better understand the relationship between reducibility and micro- and nanostructure. Combination of TPR data, Rietveld analysis of XRD diagrams and HREM/HAADF-STEM suggest that the nano-particles are responsible for Ce4+ reduction in the moderate temperature range. Results obtained in this work show that previous models based on kinetic and theoretical analysis can be fully supported by morphological characterization. This study unveils the key parameters that must be known in order to select appropriate commercial ceria samples.