Catalytic activity and selectivities of metal oxides and Pt/Al2O3 were evaluated for the combustion of NH3, which is considered a carbon-free energy source. Catalytic NH3 combustion using 3d transition metal oxides for the stoichiometric NH3-O-2 reaction showed the following order of activity: MnO2 > Co3O4 > CuO > Fe2O3 approximate to V2O5 > NiO. This order implies that the activity increases with decreasing oxygen bond energy of the metal oxides. CuO exhibited higher N-2 selectivity than the other transition metal oxides.