Active　site　structure　for　NO　decomposition　carried　out　on　perovskite-like　oxides　were　discussed　based　on　the　N2　yield　measured　from　LaSrNi　1-xAlxO4　with　different　B-site　cations　and　from　La2-ySryCuO4　with　different　crystal　phases.　Results　show　that　the　active　site　contains　two　oxygen　vacancies,　two　transition　metals,　and　one　lattice-oxygen,　with　the　oxygen　vacancy　locating　on　the　apex　of　MO6　octahedron,　and　the　lattice　oxygen　locating　between　the　two　transition　metals　(i.e.,　M-O-M　plane).　Density　functional　theory　(DFT)　analysis　to　the　structure　shows　that　this　new　active　site　is　the　most　active　structure　for　NO　adsorbing,　and　hence,　for　NO　decomposition.　The　similar　trend　of　the　relative　energies　that　are　required　for　the　formation　of　oxygen　vacancies　with　f　form　(calculated　from　DFT),　the　amount　of　oxygen　vacancies,　and　the　activities　(N2　yield)　certifies　this　result　further.　©　2007　American　Chemical　Society.