The adsorption of NO at 80 degrees C on Cu-overexchanged ZSM-5 (Si/Al = 80) has been investigated in a flow apparatus. The formation of N2O during a transient phase was observed after He pretreatment of the zeolite at 550 degrees C. A negligible amount of N2O was detected, in contrast, from Oz pretreated zeolite. The formation of N2O has been associated to the reoxidation from Cu+ to Cu2+ Of a fraction (about 40%) of copper in the zeolite. The redox chemistry in NO adsorption at low temperature can be related to the activity of Cu-ZSM-5 zeolite in NO decomposition.