Relaxation　activities　of　grain　boundary　dislocations　in　a　nanocrystalline　CrMnFeCoNi　high-entropy　alloy　were　investigated　using　in-situ　high-resolution　transmission　electron　microscopy.　1/3　＜　111　＞　Frank　dislocations　at　a　low-angle　grain　boundary　were　relaxed　by,　climbing　or　emitting　Shockley　partials　that　produced　stacking　faults　slightly　narrower　than　the　theoretically　predicted　width.　The　extended　dislocation　structures　were　quite　stable　since　no　any　change　of　the　Shockley　partial　position　or　the　stacking　fault　width　was　induced　under　further　e-beam　irradiation.　These　behaviours　indicate　easy　activation　of　Shockley　partials　and　strong　barriers　for　dislocation　motion　in　the　alloy,　which　explains　well　the　excellent　deformability　and　strengthening　effect　of　the　alloy.　In　contrast,　Frank　dislocations　at　a　twin　boundary　maintained　a　compact　core　structure,　but　were　accompanied　with　a　rotation　process　of　the　adjacent　grain.　(C)　2017　Elsevier　B.V.　All　rights　reserved.