It　is　urgent　to　develop　new　efficient　ammonia　synthesis　catalysts　using　non-precious　metals.　Herein,　the　Mo2C　species　is　introduced　into　a　carbon-supported　Mo　catalyst　by　in　situ　carburization　of　a　carbon-supported　Mo　catalyst　in　H-2.　In　combination　with　the　presence　of　the　Mo2C　phase　as　well　as　the　enhancement　of　the　graphitization　degree　of　carbon　and　the　amount　of　the　low-valent　Mo　species,　the　migration　and　the　exchange　of　the　adsorbed　species　with　the　gaseous　species　are　accelerated.　As　a　result,　the　catalyst　with　carbonization　treatment　shows　higher　ammonia　synthesis　activity　than　the　sample　without　carbonization,　and　the　ill　effect　of　the　poisoning　of　reagent　gases　also　is　alleviated.