Although　cross-slip　strongly　affects　the　deformation　of　polycrystalline　materials,　the　phenomenon　is　rarely　studied　in　twinned　face　centered　cubic　(FCC)　metals.　Here　we　performed　in-situ　TEM　nanoindentation　on　a　twinned　nickel　bi-crystal.　Multiple　pile-ups　were　generated,　with　the　first　dislocations　pinned　at　a　coherent　twin　boundary　(CTB)　and　multiple　following　dislocations　cross-slipping　within　the　matrix.　Stress　calculation　revealed　that　the　cross-slip　events　are　made　possible　by　the　CTB,　the　first　dislocations,　and　the　favorable　shear　stress　created　jointly　by　external　stress　and　dislocation　interaction.　These　cross-slip　events　reduce　tip　stress　and　soften　the　material　until　inter-grain　plasticity　is　eventually　activated.　IMPACT　STATEMENT　In-situ　TEM　nanoindentation　reveals　the　characteristics　of　dislocation　pinning,　pile-ups　and　cross-slip　along　the　twinning　boundary　in　a　twinned　FCC　metal　for　the　first　time.