Copper-manganese oxide catalysts are prepared with an atomic ratio of Cu/Mn=2/1 using a coprecipitation procedure under air atmosphere. The time of aging, i.e., the time that precipitate remains in contact with the precipitating medium, has been varied from 0 (for unaged precursor) to 300 minutes and the effect of precipitate aging time in each atmosphere upon the structure and morphology of different catalysts and their precursors is investigated. The precursors and catalysts were characterized by powder X-ray diffraction (XRD), temperature programmed reduction (TPR) and transmission electron microscopy (TEM). X-ray diffraction and electron microscopy showed that aging of the initial precursor altered the structure of the precursor. The TPR reduction profiles of the copper — manganese mixed oxide catalysts showed a dramatic change of shape on aging. In all catalysts, CuO was completely reduced to metal while the MnO did not reduce under the experimental conditions.