La-modification to copper/alumina was studied in view of possible high-temperature application as a lean-bum NOx removal catalyst. The solid-state reaction between compounds; copper, lanthanum and alumina supports at elevated temperatures was examined by X-ray diffraction (XRD) and electron spin resonance (ESR) for Cu(2 +). The formation of ’Cu-modified Al2O3’, mixed with LaAlO3, was observed at the temperature range of 850-1000 degrees C, which was characterized by XRD peaks appearing at d = 0.195-0.2, 0.241, and 0.268 nm. The evaluation of NO removal performance with C3H6 catalysts subjected to severe heat-treatment was performed under an excess of oxygen. 10 mol-% Cu-5 mol-% La-Al2O3 catalyst subjected to heat-treatment at 900 degrees C and 1000 degrees C in air showed NO removal conversion efficiencies of 14% and 13% under lean-burn conditions of A/F = 18 and S.V. = 100 000 h(-1), respectively. La-modification (5 mol-%) of an alumina support successfully helped to retain the lower temperature phase in Cu-Al2O3 system even at 1000 degrees C, and was useful to the improvement of the thermal stability of Cu-Al2O3 catalyst. A large amount (10 mol-%) of La-modification to Cu-Al2O3 system resulted in the formation of CuLaAl11O19.