The　increase　of　alumina　calcination　temperature　from　800　degrees　C　to　1300　degrees　C　results　in　the　transformation　of　gamma-Al2O3　to　alpha-Al2O3　phase　accompanying　a　decrease　of　specific　surface　area　and　the　amount　of　tetrahedral　Al3+　sites.　Over　Ru-Ba/alumina　catalysts,　an　increase　in　alumina　calcination　temperature　would　broaden　the　size　distribution　of　Ru　particles,　enlarge　the　metal-to-oxide　ratio　of　Ru,　decrease　the　amount　of　surface　hydroxyl　groups,　as　well　as　lower　the　temperature　for　N-2　desorption.　As　a　result,　the　increase　of　alumina　calcination　temperature　lessens　the　effect　of　hydrogen　poisoning　and　decreases　the　activation　energy　for　ammonia　synthesis.　The　Ru-Ba/Al2O3　catalyst　with　alumina　calcined　at　980　degrees　C　having　both　theta-Al2O3　and　alpha-Al2O3　shows　ammonia　synthesis　rate　three　times　higher　than　that　with　alumina　calcined　at　800　degrees　C　having　a　gamma-Al2O3　phase.