A　thin　film　tensile　technique　with　in　situ　atomic-scale　observations　was　developed　to　directly　characterize　the　atomic-scale　plastic　deformation　mechanisms　and　fracture　process　of　nanocrystalline　gold　thin　films.　The　grain　rotation　accompanying　the　tensile　fracture　processes　was　studied　at　the　atomic　scale.　Grain　boundary　disclination　nucleation　for　accommodating　inter-grain　rotation　plasticity　was　directly　dynamically　observed　in　situ.　These　results　appear　to　support　the　concept　of　nucleation,　growth　and　mobilization　of　disclinations　for　nanocrystalline　plasticity　by　grain　rotations.　(C)　2010　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.