M23C6　carbide　is　a　common　precipitate　phase　present　in　Ni-based　superalloys.　The　carbide　is　generally　an　alloy　carbine　and　often　contains　more　than　one　metallic　element.　In　this　study,　the　site　preference　of　metallic　elements　in　M23C6　carbide　in　a　Ni-based　single　crystal　was　determined　by　means　of　aberration-corrected　High-Angle　Annular　Dark　Field　Scanning　Transmission　Electron　Microscopy　(HAADF-STEM)　technique　and　quantitative　STEM　(QSTEM)-based　image　simulation　method.　The　carbide　was　found　to　contain　mostly　Cr　and　Re,　with　a　small　amount　of　Mo.　The　HAADF-STEM　and　QSTEM-based　simulation　analyses　indicate　that　heavy　atoms　prefer　to　substitute　Cr　at　8c　sites.