The nature of the adsorbed species on Cu-ZSM-5 (Cu-Z), Cu-Mordenite (Cu-M), and Cu-Y-zeolite (Cu-Y) was investigated by means of temperature programmed desorption (TPD). When dinitrogen monoxide (N2O) came into contact with Cu-zeolites above 573 K, the decomposition of N2O occurred accompanied by the formation of adsorbed oxygen species and adsorbed nitrogen oxide species. In the TPD runs, three O-2 desorption peaks appeared at temperatures of 623, 673, and 753 K and were named alpha-, beta-, and gamma-peaks, respectively. The O-2 desorption at the alpha- and gamma-peaks became quickly saturated after contacting N2O at 598 K, while the amount of O-2 desorbed at the beta-peak increased with time, not reaching a constant level until 120 min of exposure. The activity for the decomposition of N2O decreased with the accumulation of beta-oxygen over the catalyst. The rate of N2O decomposition depended upon the nature and amount of the copper zeolite catalysts available, as determined by the formation of alpha-and/or beta-oxygen.