Selective　oxidation　is　one　of　the　most　important　oxidation　phenomena　in　multi-phase　or　multi-component　alloys.　Complex　multi-layered　oxides　with　randomly　distributed　pores　beneath　the　outer　oxide　deeply　and　comprehensively　hamper　conventional　studies.　Multi-dimensional　structures　and　elemental　distributions　are　reconstructed　on　the　initial　oxidation　of　typical　second-　and　third-generation　Ni-based　single　crystal　superalloys　by　electron　tomography.　The　initial　oxidation　of　the　second-generation　alloy　has　a　two-layered　structure　with　an　outer　Ni-rich　oxide　layer　and　an　inner　Al-rich　oxide　layer.　The　gamma　phase　in　the　third-generation　alloy　is　easily　oxidized　to　form　a　rough　surface　with　extruded　oxide　particles.