The catalytic activity for NO decomposition, H-2-TPR, CO-TPR and O-2-TPD of various Cu/zeolites-especially mordenites- and Cu/non-zeolites with different silica/alumina ratios and frameworks were examined, The copper was loaded by impregnation of cupric nitrate solution, which was followed by redox treatment with H-2/O-2 at 500 degrees C. As a result, Cu2+ ions and copper oxide crystals were found on the external surface of the zeolite crystals. The catalytic activities for the Cu/zeolites increased with the Cu2+ content as well as with the silica/alumina ratio. For Cu/non-zeolite catalysts, however, low activity was observed in spite of the presence of Cu2+. The reducibility of Cu2+ ions and the desorptibility of extra-lattice oxygen from copper oxide located on the zeolites, which increased with the silica/alumina ratio, may be related to the catalytic activity. We observed through our study that active species for NO decomposition are not only copper ions such as Cu2+ and Cu+ but also CuO, We propose that all of them are involved in the decomposition activity which is also strongly affected by the zeolite structure.