The　distribution　of　Rhenium　(Re)　in　a　Ni-based　single-crystal　superalloy　is　studied　by　sub-angstrom　resolution　transmission　electron　microscopy　(TEM)　and　energy　dispersive　X-ray　spectroscopy　(EDS).　It　is　found　that　Re　atoms　segregate　at　the　tensile　stress　regions　near　the　interfacial　dislocation　cores,　forming　the　＂Cottrell　atmosphere＂,　and　the　segregation　process　is　facilitated　by　dislocation　pipe　diffusion.　In　situ　TEM　and　scanning　electron　microscopy　(SEM)　straining　studies　reveal　that　the　Re-decorated　dislocation　networks　along　the　phase　boundaries　act　as　mechanical　walls　that　effectively　block　dislocation　motion　and　crack　propagation.　Furthermore,　the　degree　of　Re　segregation　can　be　regulated　by　thermal　treatment.　Theoretical　analysis　demonstrates　that　this　remarkable　alloying　effect　originated　mainly　from　the　interactions　between　the　local　composition　strain　of　Re　and　the　dislocation　strains,　leading　to　significantly　stabilized　interfacial　dislocation　networks.　These　results　provide　a　new　perspective　on　understanding　the　origin　of　the　Re　effect　on　mechanical　properties　in　Ni-based　super　alloys　and　will　be　beneficial　to　both　improving　creep　properties　of　Ni-based　superalloys　and　designing　high-performance　Re-free　superalloys.　(C)　2018　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.