Although　their　mechanical　behavior　has　been　extensively　studied,　the　atomic-scale　deformation　mechanisms　of　metallic　nanowires　(NWs)　with　growth　twins　are　not　completely　understood.　Using　our　own　atomic-scale　and　dynamic　mechanical　testing　techniques,　bending　experiments　were　conducted　on　single-crystalline　and　twin-structural　Ni　NWs　(D　=　similar　to　40　nm)　using　a　high-resolution　transmission　electron　microscope　(HRTEM).　Atomic-scale　and　time-resolved　dislocation　nucleation　and　propagation　activities　were　captured　in　situ.　A　large　number　of　in　situ　HRTEM　observations　indicated　strong　effects　from　the　twin　thickness　(TT)　on　dislocation　type　and　glide　system.　In　thick　twin　lamella　(TT＞　similar　to　12　nm)　and　single-crystalline　NWs,　the　plasticity　was　controlled　by　full　dislocation　nucleation.　For　NVVs　with　twin　thicknesses　of　similar　to　9　nm　＜　TT　＜　similar　to　12　nm,　full　and　partial　dislocation　nucleation　occurred　from　the　free　surface,　and　the　dislocations　glided　on　multiple　systems　and　interacted　with　each　other　during　plastic　deformation.　For　NWs　with　twin　thicknesses　of　similar　to　6　nm　＜　TT　＜　similar　to　9　nm,　partial　dislocation　nucleation　from　the　free　surface　and　the　gliding　of　those　dislocations　on　the　plane　that　intersected　the　twin　boundaries　(TBs)　were　the　dominant　plasticity　events.　For　the　NWs　with　twin　thicknesses　of　similar　to　1　nm　＜　TT　＜　similar　to　6　nm,　the　plasticity　was　accommodated　by　a　partial　dislocation　nucleation　process　and　glide　parallel　to　the　TBs.　When　TT　＜　similar　to　1　nm,　TB　migration　and　detwinning　processes　resulting　from　partial　dislocation　nucleation　and　glide　adjacent　to　the　TBs　were　frequently　observed.　(C)　2015　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.