Experiments and ab initio calculations have been performed to study the catalytic activity of calcium oxide and magnesium oxide toward N2O decomposition. The experiments were carried out in a fixed-bed quartz reactor in the temperature range 773-1223 K. The decomposition of N2O appeared to be a first-order reaction with activation energies of 26 kcal/mol for CaO and 36 kcal/mol for MgO, respectively. The decomposition rate did not change when excess oxygen was introduced to the inlet gas. The ab initio energy barriers of the dissociative reaction : N2O(g) + O-surf(2-), --> N-2(g) + O-2,surf(2-),,, in which the oxygen anion is seated in a CaO(100) or MgO(100) model surface, are 22 and 33 kcal/mol. High-temperature preexponential factors and activation energies are estimated from transition-state theory and collision theory expressions. The values agree well with those obtained experimentally. This indicates that most of the surface anions of both CaO and MgO are active in decomposing N2O in the temperature range investigated. A model of a plug-flow reactor is used to demonstrate that the temperature dependence of the overall reaction rate obtained at high N2O concentrations reflects the regenerating process of the surface and not the molecular dissociation of N2O.