The catalytic properties of Cu-exchanged H-ZSM-5 (Si/Al = ca, 80) in NO decomposition were investigated, It was found that, both in the presence and in the absence of oxygen in the feed, the rate of NO decomposition increased with the copper content up to about 640% Cu over-exchange, while the turnover frequency reached a maximum value at about 500% over-exchange, The reaction order of NO decomposition in the absence of O-2 was 1.6 in the range of NO concentration from 1000 to 5000 ppm, Addition of 1% O-2 in the feed resulted in the decrease of NO conversion to N-2 depending on the contact time, In all the range of Cu% exchange the catalysts were active for the catalytic oxidation of NO to NO2, reaching the equilibrium conversion both in the absence (above 350 degrees C) and in the presence (above 300 degrees C) of O-2 in the feed.