Cobalt-based　catalysts　are　ideal　for　CO2　reduction　reaction　(CO2RR)　due　to　the　strong　binding　and　efficient　activation　of　CO2　molecules　on　cobalt.　However,　cobalt-based　catalysts　also　show　low　free　energy　of　hydrogen　evolution　reaction　(HER),　making　HER　competitive　with　CO2RR.　Therefore,　how　to　improve　the　product　selectivity　of　CO2RR　while　maintaining　the　catalytic　efficiency　is　a　great　challenge.　Here,　this　work　demonstrates　the　critical　roles　of　the　rare　earth　(RE)　compounds　(Er2O3　and　ErF3)　in　regulating　the　activity　and　selectivity　of　CO2RR　on　cobalt.　It　is　found　that　the　RE　compounds　not　only　promote　charge　transfer　but　also　mediate　the　reaction　paths　of　CO2RR　and　HER.　Density　functional　theory　calculations　verify　that　the　RE　compounds　lower　the　energy　barrier　of　*CO　→　CO　conversion.　On　the　other　hand,　the　RE　compounds　increase　the　free　energy　of　HER,　which　leads　to　the　suppression　of　HER.　As　a　result,　the　RE　compounds　(Er2O3　and　ErF3)　improve　the　CO　selectivity　of　cobalt　from　48.8　to　69.6%,　as　well　as　significantly　increase　the　turnover　number　by　a　factor　of　over　10.　©　2023　American　Chemical　Society.