The　role　of　a　surface　oxygen　vacancy　in　the　N2O　dissociation　over　a　Cu2O　surface　was　studied　using　density　functional　theory　-　generalized　gradient　approximation　periodic　calculations.　To　perform　this　study,　surface　slab　model　-　Cu2O(111)-(√3　×　√3)R30°　surface　cell　was　used.　The　results　indicated　that　N2O　adsorption　properties　were　associated　with　the　surface　oxygen　vacancies.　The　presence　of　a　surface　oxygen　vacancy,　prepared　by　removing　one　OSUF　atom　from　(√3　×　√3)R30°　supercell,　makes　the　N2O　decomposition　possible,　which　was　believed　to　occur　at　a　oxygen　vacancy　site.　The　N　2O　decomposition　at　the　surface　oxygen　vacant　site　depends　on　whether　the　molecule　is　adsorbed　with　the　O-　or　N-end　on　a　vacancy.　For　the　first　case,　the　reaction　proceeds　spontaneously,　which　leads　to　an　ejection　of　N　2　from　the　surface　and　the　rest　of　the　oxygen　atoms　occupying　the　vacancy.　In　the　second　case,　even　though　there　is　an　elongation　of　both　N-N　and　N-O　bonds,　the　dissociation　is　unfeasible　due　to　very　small　adsorption　energy　and　high　activation　energy.　The　role　of　the　defective　surface　with　surface　oxygen　vacancy　is　to　provide　electrons　to　the　adsorbed　molecule.　©　2008　World　Scientific　Publishing　Company.