Catalytic reduction of NO by CO was studied over La2-xBaxCuO4 (x = 0.0 or 0.4) mixed oxides prepared by coprecipitation method. The catalysts were characterized by X ray diffraction (XRD), O-2 temperature-programmed desorption (O-2-TPD), H-2 temperature-programmed reduction (H-2-TPR) and X-ray absorption near edge structure (XANES). NO + CO reaction was carried out in a fixed-bed flow reactor, from room temperature to 500 degrees C, at atmospheric pressure. Both fresh catalysts were active for the NO + CO reaction but when were submitted to thermal aging, the barium free catalyst significantly lost its activity. The partial substitution of La by Ba enhanced the thermal stability and although the activity of the catalyst has decreased, it remains high, approaching 100 % at 500 degrees C. These results can be associated with reducible copper species observed by XANES in the thermal aged catalyst containing Ba.