Copper manganese oxides are prepared using a coprecipitation procedure and studied for the oxidation of CO at ambient temperature. In particular, the effect of a range of preparation variables are investigated in detail. The variables investigated include the precipitate ageing time, pH and temperature of precipitation : the [Cu]/[Mn] ratio of the precipitation solution and the catalyst calcination temperature. The optimum preparation conditions are identified with respect to the catalyst activity for the oxidation of CO at ambient temperature. The results are interpreted in terms of the structure of the active catalyst. Generally it has been concluded that catalysts containing copper/manganese mixed phases are found to be the most active.