Catalysts that have been extensively investigated for direct soot oxidation in Catalyzed Diesel Particulate Filters (CDPFs) are very often based on mixed oxides of ceria with zirconia, materials known to assist soot oxidation by providing oxygen to the soot through an oxidation-reduction catalytic cycle. Besides the catalyst composition that significantly affects soot oxidation, other parameters such as morphological characteristics of the catalyst largely determined by the synthesis technique followed, as well as the reagents used in the synthesis may also contribute to the activity of the catalysts. In the present work, two ceria-zirconia catalyst samples with different zirconia content were subjected to different milling protocols with the aim to shift the catalyst particle size distribution to lower values. The produced catalysts were then evaluated with respect to their soot oxidation activity following established protocols from previous works. A previously developed multi-population kinetics model was employed to describe quantitatively the soot oxidation process and assess the effect of catalyst particle size (for each composition) on the kinetic parameters. In general, the intrinsic reactivity of a given catalytic material can be significantly enhanced through appropriate morphological and structural modulation. Such a step is a prerequisite for any subsequent development of CDPFs based on any catalytic material.