Ni/CeO2-ZrO2 solid solutions are well known by their promissory catalytic role in hydrogen production processes such as reforming and partial oxidation of hydrocarbons. CeO2-ZrO2 support can effectively disperse Ni particles and donate oxygen promoting Ni active phase resistance to poisoning by carbon deposition. Thus, in this work we study the influence of Ni on oxygen vacancy formation on the Ce0.7Zr0.25O2(111) surface, by using the density functional theory (DFT) approach with the Hubbard's correction (U) for Ce(4f) electrons. We performed DFT+U energetic calculations on Ni/Ce0.75Zr0.25O2 (Ni is adsorbed over an O-O bridge site) and Ni-Ce0.75Zr0.25O2 (Ni is inserted into the slab) systems, with an O-vacancy. Moreover, we analyzed the electronic structures of these solids by drawing their spin polarized density of states (DOS) plots. Our results indicate that Ni insertion between two O subsurface layers facilitates Ce0.75Zr0.25O2 mixed oxide reduction and enhances its ionic mobility and oxygen donation properties. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.