Nitric oxide and nitrogen dioxide were found during the thermal desorption of surface species left on Fe-ferrierites after the decomposition of nitrous oxide. This demonstrates the formation of surface NOx species during N2O decomposition. Repeated decomposition and subsequent desorption of surface species confirm the active role of surface NOx species. Addition of NO up to a fraction of 0.1 times the amount of N2O increased the decomposition of nitrous oxide as well as the amount of surface NOx species. The use of nitrous oxide labeled with O-18 demonstrated that the zeolite oxygens participate in the reaction and that the presence of NO enhances this participation.