Spinel oxide (Mn3O4) 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 CO2 chemisorption measurement. The catalytic activity of as prepared Mn3O4/hexaaluminate composites for methane combustion was evaluated as functions of the Mn3O4 loading and the metal composition of the spinel surface layer. It was revealed that the air oxidation-derived composites showed the excellent specific activities superior to those of the corresponding Mn3O4/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.