The activity of the mixed copper–manganese oxides CuO–MnO x (1.5<x<2), obtained by coprecipitation and activated at 300°C, has been studied for CO–NO and CO–NO–O 2 reactions. As shown by magnetic susceptibility data, X-ray diffraction, FTIR spectra, and catalytic tests, an interaction between CuO and MnO x with formation of a disordered mixed oxide with a spinel-like structure is the cause of the high activity of CuO–MnO x samples.At ambient temperature (25°C) both adsorption and interaction of CO and NO become more intense with increasing atomic fraction of copper content Cu/Cu+Mn up to 0.53 (catalyst C5M5). For the most active sample C5M5, the degree of NO conversion to N 2 attained with a CO+NO+O 2 +Ar mixture is almost the same as that obtained with a CO+NO+Ar mixture. A Langmuir–Hinshelwood mechanism is proposed for both (CO–NO and CO–NO 2 ) interactions at ambient temperature.With increasing temperature under the conditions of a CO+ NO+Ar mixture, reduction of the catalyst surface starts. This leads in turn to depression of the CO–NO reaction at temperatures up to 130°C (low-temperature region) and to progressive acceleration of the CO–NO reaction at temperatures above 130°C (middle-temperature region). In the presence of oxygen (a CO+NO+O 2 +Ar mixture), CuO–MnO x catalysts have an even higher activity over a wide temperature range (75–300°C).