The coating of Mn-substituted hexa-aluminate catalysts (BaMnAl11O19-alpha and Sr0.8La0.2MnAl11 O19-alpha) on alpha-SiC substrates was investigated for high temperature application above 1000 degrees C. The thermal stability of the hexa-aluminate catalyst films on the alpha-SiC substrates was significantly affected by reactivity between the oxidized layer (SiO2) of the surfaces of the substrates and the coated layers. The Mn-substituted hexa-aluminate films were thermally less stable due to their high reactivity than unsubstituted hexa-aluminates, The Sr0.8La0.2MnAl11O19-alpha film directly coated on the substrate exfoliated from the substrate even after heating at 1200 degrees C due to its high reactivity to the SIO2 layer, whereas the BaMnAl11O19-alpha film was stable after the same treatment. The thermal stability of the Mn-substituted hexa-aluminate film could be improved by insertion of an Al6Si2O13 intermediate layer between the film and the SIC substrate. Additional coating of a highly crystallized Ba0.75Al11.0O17.25 intermediate layer underneath the BaMnAl11O19-alpha catalyst layer was also effective. The Al6Si2O13 and Ba0.75Al11.0O17.25 intermediate layers suppressed the diffusion of SiO2 from the substrate and subsequent reaction between SiO2 and the hexa-aluminate film.