Barium hexaaluminates partially substituted by copper have been synthesized by a sol-gel method. Formation of the parent BaAl12O19 and the mixed BaCuAl11O18.5 catalysts occurred during calcination at 1200 degrees C. XRD showed a good crystallinity of the structure and expansion of the unit cell parameter due to the presence of larger Cu2+ ions in place of Al3+ in tetrahedral sites. The presence of copper strongly enhances the catalytic activity in methane combustion, which should be due to the Cu2+ species evidenced by FTIR of adsorbed CO and by TPR. The introduction of a second copper ion in the structure was not possible, however, as revealed by the formation of copper (II) aluminate in addition to the Cu-substituted hexaaluminate phase.