Titanium　and　its　alloys　have　been　widely　used　in　automotive　industry　and　aerospace　field　due　to　their　high　mechanical　strength　and　low　density.　It　has　been　known　that　α-Ti　has　an　hcp　crystal　structure　and　silp　in　hcp　structure　is　limited　because　of　only　3　independent　slip　systems.　Therefore,　twinning　is　active　in　hcp　structure　and　the　deformation　behavior　of　hcp　metals　is　very　complex　by　the　presence　of　both　dislocation　slip　and　twinning.　In　sub-micron　sized　α-Ti　sample,　deformation　twins　are　difficult　to　produce　and　the　deformation　mechanism　is　mainly　dislocation　slip.　However,　it　is　hard　to　identify　the　activated　dislocation　slip　system　in　α-Ti,　as　a　few　avaliable　slip　planes　is　corresponding　to　one　slip　direction.　Usually　there　are　two　ways　to　identify　the　activated　slip　systems.　One　is　to　deduce　the　slip　plane　and　the　slip　direction　based　on　the　loading　direction　and　the　crystal　orientation.　But　this　method　is　not　accurate　because　of　many　possible　groups　of　slip　planes　and　slip　directions　in　hcp　structure.　The　other　one　is　judging　the　Burgers　vector　of　the　dislocation　under　certain　diffraction　vectors　based　on　Bragg＇s　law　by　using　TEM.　It　takes　time　and　can　only　determine　the　slip　direction　of　dislocation.　Therefore,　it　is　important　to　find　an　effective　method　to　identify　the　active　slip　system　more　simply　and　accurately　during　deformation　process.　In　this　work,　a　nanometer　sized　tensile　sample　of　α-Ti　single　crystal　was　fabricated　by　using　focused　ion　beam　(FIB)　technique.　In　situ　tensile　test　was　carried　out　along　[21̄1̄0]　of　α-Ti　sample　by　using　a　homemade　bimetal　stretching　device　in　TEM.　It　has　been　found　that　three　types　of　the　dislocations,　one　prismatic　　dislocation　and　two　pyramidal　　dislocations,　were　activated　in　order　with　strain　increasing　during　tensile　process.　The　Burgers　vectors　of　dislocations　were　determined　by　two-beam　diffraction　contrast　imaging　in　TEM.　For　hcp　structure,　one　Burgers　vector　may　have　the　characteristics　of　a　variety　of　slip　planes.　By　EBSD　technique,　the　crystalline　orientation　and　the　loading　direction　in　TEM　were　indexed　accurately　and　Schmid　factors　for　all　the　possible　slip　systems　were　calculated　corresponding　to　each　Burgers　vector.　Then,　the　activated　slip　systems　during　in　situ　TEM　tensile　process　are　determined　by　Burgers　vector　and　Schmid　factor.　This　work　offers　an　effective　method　to　identify　the　activated　slip　system　during　tensile　process　and　get　more　understanding　about　the　plastic　deformation　mechanism　of　α-Ti　and　hcp　metals.　KEYWORDS　©　All　right　reserved.