The Ta₂O₅ or Ta (99.99%, Aldrich Chemical Co. Ltd.) was carburized using pure CH₄ by temperature-programming. The BET surface areas of these materials varied with different molar hourly space velocity, suggesting that the sorption properties of these materials were strong functions of space velocity employed. The tantalum carbides proved to be active NH₃ decomposition catalysts. The ammonia decomposition activities of tantalum carbides normalized by the oxygen uptake increased with increasing surface area, suggesting that NH₃ decomposition over these materials is structure-sensitive. It is considered that the structure-sensitivity over tantalum carbides may be due to variations in the surface stoichiometry with surface area. Activities of the tantalum carbides were comparable or superior to those of vanadium carbide and nitride catalysts, while tantalum carbides had activities that were higher by a factor of 94 than Pt/C catalyst.