Oscillations occuring in the catalytic decomposition of N2O into the elements over Cu-ZsM-5 were studied at 698 K in integral and gradientless reactors. Transient experiments by using step changes in the nitrous oxide concentration were employed to determine the amounts of adsorbed species in different phases of the oscillations. The experimental results can be modelled by a scheme of five reactions. The proposed reaction mechanism includes the dynamic interaction of two adsorbed species, atomic oxygen and NO3, and explains the crucial role of nitric oxide, which is formed in a slow side reaction. The results suggest that monovalent copper is the active site for the decomposition of N2O, and that this species is involved in a redox cycle.