Introduction　of　alkaline　earth　metal　oxide　(AEMO)　into　TiO2　was　found　to　promote　CO　oxidation　(in　the　order　BaO＞SrO＞CaO＞MgO)　over　Au　nanoparticles　supported　on　TiO2.　From　experimental　(electron-transfer　reaction,　CO　electrochemical　oxidation,　CO　adsorption　and　Mott-Schottky　plots)　and　theoretical　(density　functional　theory)　calculations,　it　is　proposed　that　AEMO　may　act　as　an　electron　promoter　for　CO　oxidation,　but　not　as　an　exclusive　structural　promoter　as　widely　regarded.　Introduction　of　AEMO　raises　the　Fermi　level　of　the　TiO2　support,　resulting　in　an　enhanced　electron　transfer　from　the　support　to　the　Au　sites　and　promoting　activation　of　CO　adsorbed　at　Au　sites.　Moreover,　the　enhanced　catalytic　activities　induced　by　AEMO　depend　on　the　increase　in　the　Fermi　level　of　the　support　in　the　order:　TiO2-BaO＞TiO2-SrO＞TiO2-CaO＞TiO2-MgO.　This　investigation　provides　a　new　insight　to　understand　the　role　of　the　electron　promoters　in　the　thermocatalytic　reactions.　(C)　2015　Elsevier　B.V.　All　rights　reserved.