The solid-state reaction and hydrocarbon-removal activities of composite powders in the system of CuO and La-modified Al2O3 were studied for the purpose of their application to heat-stable catalyst in exhaust-treatment. X-ray diffraction revealed the formation of catalytic nanocomposite-powder of CuLaAl11O19 and γ-Al2O3 at 1100 °C from the solid-state reaction between γ-Al2O3, CuO and La2O3. The La-modification of γ-Al2O3 was effective to maintain the large surface areas of these composite powders. The C6H6 removal activities were compared with practical automotive catalyst in the system of Pt–Ce and γ-Al2O3. The composite-powder of CuLaAl11O19 and γ-Al2O3 is active for complete oxidation of benzene and the microstructure is favourable as a powder for catalytic coat-layer.