Metal　oxides,　as　one　of　the　mostly　abundant　and　widely　utilized　materials,　are　extensively　investigated　and　applied　in　environmental　remediation　and　protection,　and　in　energy　conversion　and　storage.　Most　of　these　diverse　applications　are　the　result　of　a　large　diversity　of　the　electronic　states　of　metal　oxides.　Noticeably,　however,　many　metal　oxides　present　obstacles　for　applications　in　catalysis,　mainly　due　to　the　lack　of　efficient　active　sites　with　desired　electronic　states.　Here,　the　fabrication　of　single-tungsten-atom-oxide　(STAO)　is　demonstrated,　in　which　the　metal　oxide＇s　volume　reaches　its　minimum　as　a　unit　cell.　The　catalytic　mechanism　in　the　STAO　is　determined　by　a　new　single-site　physics　mechanism,　named　as　quasi-atom　physics.　The　photogenerated　electron　transfer　process　is　enabled　by　an　electron　in　the　spin-up　channel　excited　from　the　highest　occupied　molecular　orbital　to　the　lowest　unoccupied　molecular　orbital　+1　state,　which　can　only　occur　in　STAO　with　W5+.　STAO　results　in　a　record-high　and　stable　sunlight　photocatalytic　degradation　rate　of　0.24　s(-1),　which　exceeds　the　rates　of　available　photocatalysts　by　two　orders　of　magnitude.　The　fabrication　of　STAO　and　its　unique　quasi-atom　photocatalytic　mechanism　lays　new　ground　for　achieving　novel　physical　and　chemical　properties　using　single-metal-atom　oxides　(SMAO).