Metal-peroxo species on oxides are recognized as important intermediates for catalytic reactions on oxides. In this work, surface structures of stoichiometric and non-stoichiometric yttria stabilized zirconia (YSZ) were investigated for the low index surfaces (111), (110), and (100) by using first principles electronic structure calculations, and the energetic stabilities of non-stoichiometric surfaces with respect to the stoichiometric ones were calculated as a function of oxygen chemical potential. In the oxygen-rich condition, a unique form of zirconium-peroxo embedded in the lattice oxygen sites was found in YSZ(110); the embedded peroxo was recently confirmed in experimental observations for TiO2 anatase (101) (M. Setvin et al., Science 341 (2013) 988) and cubic In2O3 (001) (D. R. Hagleitner et al., Phys. Rev. B 85 (2012) 115441). The electronic structure of the embedded peroxo found in O-rich YSZ(110) was analyzed in details by means of orbital energy diagrams and density of states. (C) 2015 Elsevier B.V. All rights reserved.