The　high　quality,　high　purity　and　large　size　Lanthanum　hexaborides　(　LaB6　)　single　crystals　have　been　successfully　grown　by　optical　floating　zone　method.　The　optimum　crystal　growth　parameters　are　listed　as　follow:　sample　rotation　rate　is　30　r/min　and　the　growth　rate　is　8-10　mm/h.　The　largest　thermionic　emission　current　density　of　(　100　)　crystal　surface　is　44.　36　A/cm(2)　at　1873　K.　The　work　function　at　absolute　zero　is　calculated　to　be　1.　99　eV　by　Richardson　line　method,　and　the　average　value　of　effective　work　functions　at　different　temperatures　are　calculated　to　be　2.　59　eV.　The　field　emission　characteristic　of　single　crystal　LaB6　field　emitting　single　tip　show　that　the　maximum　field　emission　current　density　is　4.　9　x　10(6)　Acm(-2)　and　the　field　enhancement　factor　is　calculated　to　be　41500　cm(-1),　indicating　excellent　field　emission　performance.　Thus,　the　single　crystal　is　a　promising　cathode　material　for　practical　applications　regarding　to　its　excellent　thermionic　emission　or　field　emission　properties.