The　development　of　a　Ru　catalyst　with　excellent　ammonia　synthesis　performance　plays　a　key　role　in　the　application　of　ammonia　in　the　upcoming　renewable　energy　era.　Herein,　a　ceria-supported　Ru　catalyst　was　prepared　by　oxygen-induced　activation,　resulting　in　enhancement　of　the　amount　of　the　exposed　Ru　species,　active　oxygen　species,　and　Ru-O-Ce　bond.　As　a　result,　the　amount　of　Ru　species　surrounded　by　active　oxygen　species　would　be　enhanced,　facilitating　the　exchange　and　reaction　of　the　hydrogen　species　adsorbed　on　the　Ru　catalyst　with　the　gaseous　reactants.　Oxygen-induced　activation　of　the　ceria-supported　Ru　catalyst　leads　to　enhancement　of　the　ammonia　synthesis　activity　by　more　than　63%;　moreover,　the　as-obtained　catalyst　has　a　smaller　negative　reaction　order　of　H2　than　its　Ru/CeO2　counterpart.