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°C. As a result, Cu 2 + 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 Cu 2 + 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 Cu 2 + . The reducibility of Cu 2 + 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 Cu 2 + 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.