The　microstructures　of　ternary　Ni-Al-Re　and　quaternary　Ni-Al-Re-Ru　single-crystal　alloys　were　investigated　at　atomic　and　electronic　levels　to　clarify　the　synergistic　effect　of　Re　and　Ru　in　nickel-based　singlecrystal　superalloys.　In　the　Ni-Al-Re　alloy,　it　was　directly　observed　that　Re　atom　occupied　the　Al　site　of　gamma＇　phase.　In　the　Ni-Al-Re-Ru　alloy,　the　mechanisms　of　Re　repartition　between　gamma　and　gamma＇　phases　were　proposed.　In　the　dendritic　cores,　high　concentrations　of　Re　exceeded　the　solubility　limit　of　gamma＇　phase　and　partitioned　to　gamma　phase,　which　led　to　the　homogenization.　In　the　interdendritic　regions,　Ru　resulted　in　the　repartitioning　of　Re　to　gamma　phase　which　was　proved　by　transmission　electron　microscopy　and　first-principles　calculations.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.