Oxidation　is　a　key　drawback　in　the　high　temperature　performance　of　superalloys,　and　it　is　scientifically　and　technologically　important　to　determine　its　atomic　scale　oxidation.　In　this　study,　the　oxidation　mechanism　of　a　gamma/gamma＇　structured　Co80Al7W8Ti4Ta1　single　crystal　superalloy　was　studied　in　situ　down　to　the　nano　and　atomic　scales　by　directly　inspecting　the　oxidation　process　in　an　environmental　transmission　electron　microscope.　The　oxidation　priority　follows　the　order　gamma　phase　＞　gamma/gamma＇　boundary　＞　gamma＇　phase,　indicating　selective　phase　oxidation.　In　situ　selective　phase　and　elemental　oxidation　behaviours　provide　insight　for　the　design　of　oxidation　resistive　superalloys.