A　series　of　MgAl-layered　double　oxides　(LDO)　doped　with　different　rare-earth　elements　(Y,　La,　and　Ce)　were　synthesized　by　the　calcination　of　Mg-Al　layered　double　hydroxides,　and　Ru,　which　were　used　to　prepare　ammonia　synthesis　catalysts.　The　as-obtained　oxides　and　catalysts　were　characterized　by　XRD,　TEM,　TPD,　TPR　and　XPS　to　understand　their　catalytic　performances　in　ammonia　synthesis.　The　H-2-TPR　and　HRTEM　studies　reveal　that　Ru/Y-LDO　catalyst　possesses　more　active　Ru　metal　and　small　particle　size.　The　XPS　demonstrates　that　the　electronic　interaction　between　Y　and　Ru　metals　is　stronger,　which　can　be　tentatively　explained　by　most　of　Y　inserted　into　the　hydrotalcites　structure.　CO2-TPD　demonstrates　that　Ru/Y-LDO　catalyst　shows　stronger　basic　site　densities　than　catalysts　doped　with　Ce　and　La.　Higher　activity　of　the　Ru/Y-LDO　catalyst　can　be　attributed　to　smaller　particle　size,　more　active　metal　(Ru)　and　strong　Ru-support　interaction.　(c)　2018　Published　by　Elsevier　B.V.　on　behalf　of　Chinese　Society　of　Rare　Earths.