In　situ　atomic-scale　bending　tests　of　twin-structured　Ni　nanowires　were　realised　using　a　homemade　deformation　device.　The　results　showed　that　the　plastic　deformation　mechanism　in　twin-structured　Ni　nanowires　depended　on　the　deformation　stage.　At　the　early　stages　of　bending　deformation,　the　plasticity　of　twin-structured　Ni　nanowires　was　controlled　by　dislocations　interacting　with　the　twin　boundaries　or　parallel　to　them.　With　increasing　bending　strain,　both　dislocation　and　face-centred　cubic-body-centred　tetragonal　phase　transition　occurred.　At　very　high　bending　strain,　grain　boundaries　resulting　from　the　lattice　distortion/collapse　were　formed.　This　study　details　the　deformation　mechanisms　of　the　twin-structured　Ni　nanowires　under　bending　deformation,　which　advances　the　basic　understanding　of　the　plasticity　mechanisms　in　metals.