The　structures　and　electronic　properties　of　(WO3)3　nanoclusters　adsorption　on　defective　MgO　ultrathin　films　on　Ag(001)　have　been　investigated　by　means　of　density　functional　theory　(DFT)　calculations　including　dispersion　interactions.　Our　results　show　that,　after　deposition,　the　oxygen　vacancy　on　the　defective　MgO/Ag(001)　films　is　healed　by　one　terminal　oxygen　atom　of　the　(WO3)3　clusters　through　forming　four　O-Mg　bonds.　The　conformation　of　the　(WO3)3　nanoclusters　is　distorted　slightly　and　the　W3O3　cyclic　conformation　of　adsorbed　(WO3)3　nanoclusters　is　still　maintained.　The　defective　MgO/Ag(001)　2D　films　lead　to　enhancement　of　the　adsorption　energy　between　the　(WO3)3　clusters　and　the　substrates,　compared　to　that　on　defect-free　MgO/Ag(001)　2D　films　and　a　defective　MgO(001)　surface.　It　is　interesting　that　obvious　charge　transfer　(2.74e)　occurs　from　the　defective　MgO/Ag(001)　films　to　the　5d　empty　state　of　the　(WO3)3　clusters,　which　mainly　originated　from　spontaneous　electron　tunneling　through　the　thin　MgO　dielectric　barrier,　and　less　from　the　surface　defective　state　as　the　consequence　of　the　formation　of　O-Mg　adsorption　dative　bonds　at　the　interface.　In　addition,　compared　with　(WO3)3　nanoclusters　in　the　gas　phase,　on　the　defect-free　MgO/Ag(001)　2D　films　and　the　defective　MgO(001)　surface,　different　scanning　tunneling　microscopy　images　and　vibrational　spectra　for　depositing　(WO3)3　nanoclusters　are　observed,　which　could　help　in　the　identification　of　(WO3)3　nanocluster　adsorption　on　the　defective　MgO/Ag(001)　ultrathin　films　in　future　experiments.　As　a　consequence,　our　results　reveal　that　(WO3)3　nanoclusters　adsorption　on　defective　MgO/Ag(001)　ultrathin　films　provide　a　new　avenue　to　tune　and　modify　the　charge　state　and　chemical　reactivity　of　tungsten　oxide　nanoclusters.　©　2017　The　Royal　Society　of　Chemistry.