Cu2Ag2O3 has been prepared by a precipitation method and evaluated for ambient temperature carbon monoxide oxidation. The Cu2Ag2O3 catalyst demonstrated appreciable activity and a relationship with preparation ageing time was observed. An ageing time of 4 h produced a catalyst with the highest oxidation performance. The catalyst precursor materials, prepared by drying at room temperature, displayed initial high activity, which decreased with time on line. The precursors were transformed during CO oxidation to form the mixed oxide Ci(2)Ag(2)O(3) as the material was dried in situ. A comparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu2Ag2O3, aged for 4 h was at least as active as the hopcalite catalyst. (c) 2006 Elsevier B.V. All rights reserved.