Hydrothermal synthesis by using urea hydrolysis at 1.0-3.0MPa and 120-130 ℃ was employed to prepare Mn-substituted hexaaluminate catalysts for methane combustion. The results from DTA-MS demonstrated that CO3(2-) and OH(-) anions co-exist in the hydrothermal reaction. XRD reveals that the components of carbonates and hydroxides in the hydrothermal reaction are more favorable than those in the (NH4)2CO3 co-precipitation for the formation of the Mn-substituted hexaaluminate phase. After calcination at 1,200 ℃ for 2 h, LaMnAl11O19 is the major phase of the catalyst prepared by the hydrothermal synthesis method while LaAlO3 is the major one of the catalysts prepared by NH4OH and (NH4)2CO3 co-precipitation. The catalyst prepared by hydrothermal synthesis has higher activity than that prepared by NH4OH and (NH4)2CO3 co-precipitation. The major reason is that more Mn(2+) ions have incorporated into the hexaaluminate lattice. The effect of drying methods on the formation of hexaaluminate phase was also discussed.