This study investigates a potential synergy between Ag nanoparticles and Yttria-Stabilized Zirconia (YSZ), an oxygen ionically conducting support, for developing an efficient and stable catalyst for Diesel Particulate Filter regeneration only with oxygen. The catalytic performances as well as the mechanism for soot combustion were thoroughly analyzed through Temperature-Programmed Oxidation and isotopic experiments. We found that Ag/YSZ catalysts reach the highest activity for low contents of Ag, i.e. 2 wt%. Isotopic experiments were carefully performed to prove that active oxygen species originate from YSZ lattice. Silver was shown to promote soot oxidation activity by activating the dissociative adsorption of oxygen that can replenish the YSZ support.