Reducibility and characteristics of CeO 2 , ␥-Al 2 O 3 , CuO/CeO 2 , CuO/␥-Al 2 O 3 and ceria-modified CuO/␥-Al 2 O 3 catalysts were examined using a microreactor-GC NO + CO reaction system and the methods of BET, XRD, TPR, XPS and NO-TPD. The results showed that the catalytic activities of CuO/CeO 2 and CuO/␥-Al 2 O 3 were increased compared to that of CeO 2 or ␥-Al 2 O 3 alone, probably due to the presence of the copper oxide species with low valence and surface dispersion. There were two TPR peaks of CuO/CeO 2 , a low-temperature peak due to the reduction of highly dispersed copper oxide species and a high-temperature peak due to the reduction of bulk CuO. CuO/␥-Al 2 O 3 had one TPR peak, while the CeO 2 -modified CuO/␥-Al 2 O 3 had three reduction peaks with one low-temperature peak and two high-temperature peaks. The Cu 2p 3/2 (eV) binding energy of 5.0 wt.% CuO/CeO 2 was 932.79 to 934.11 eV, compared to that of CuO/␥-Al 2 O 3 equal to 935.0 eV. After added with CeO 2 , the Cu 2p 3/2 (eV) binding energy was 934.1 eV, slightly lower than the Cu 2p 3/2 (eV) binding energy. During the thermal desorption of NO, five desorption species (NO, N 2 O, N 2 , O 2 and NO 2 ) were adsorbed on CeO 2 and ␥-Al 2 O 3 but only four desorption species (NO, N 2 O, N 2 and NO 2 ) adsorbed on CuO/CeO 2 and CuO/␥-Al 2 O 3 . Two adsorbing states of NO were observed on the catalyst's surface, the weak one at low temperatures and the strong one at high temperatures. The NO-TPD profile also showed that peak temperatures of NO desorption by the catalysts were lower than that by the supports, indicating that the NO decomposition activity of the catalysts was higher than that of the supports.