The　construction　of　twin　boundaries　(TBs)　in　materials　is　a　remarkable　way　of　promoting　their　strength　and　ductility.　However,　the　effects　of　TB　orientation　on　the　mechanical　properties　have　not　been　reported　experimentally　so　far.　Using　a　state-of-the-art　in　situ　tensile　stage　equipped　in　a　transmission　electron　microscope,　uniaxial　tensile　tests　were　performed　on　three　single-crystalline　Ni　samples　with　TB　parallel　and　perpendicular　to　the　tensile　direction　and　no　TB.　The　results　showed　that　the　uniform　tensile　elongation　strongly　depends　on　TB,　120%　for　the　perpendicular　TB　sample,　99%　for　the　parallel　TB　sample,　and　only　55%　for　the　no　TB　sample.　In　addition,　dislocation　interaction　before　reaching　the　perpendicular　CTB　contribute　to　cross-slip　and　dynamic　formation　of　dislocation　jogs,　thereby　improving　strain　hardening　and　resulting　in　a　large　uniform　tensile　elongation.　(c)　2022　The　Authors.　Published　by　Elsevier　Ltd.　This　is　an　open　access　article　under　the　CC　BY-NC-NDlicense　(http://creativecommons.org/licenses/by-nc-nd/4.0/).