Spinel oxide (Mn 30 4) surface layers were produced on hexaaluminate microcrystals by means of the air-oxidation process. The surface layer completely covered the basal plane of hexagonal facets as evident from HREM observation and CO 2 chemisorption measurement. The catalytic activity of as prepared Mn 30 4/hexaaluminate composites for methane combustion was evaluated as functions of the Mn 30 4loading and the metal composition of the spinel surface layer. It was revealed that the air oxidationderived composites showed the excellent specific activities superior to those of the corresponding Mn 30 4/hexaaluminates prepared from the conventional evaporation-to-dryness process. Partial substitution of Fe for Mn of the surface layer was effective in enhancing combustion activity in a whole temperature range.