Large-sized　and　high-quality　cerium　hexaboride　(CeB6)　single　crystals　are　successfully　grown　by　the　optical　floating　zone　method.　The　structure,　chemical　composition　and　thermionic　emission　properties　of　the　crystal　are　characterized　by　x-ray　diffraction,　x-ray　fluorescence　and　emission　measurements,　respectively.　Based　on　the　observation　of　single　crystal　diffraction,　the　relative　density　of　feed　rods　has　a　great　effect　on　the　quality　of　the　grown　crystal.　The　thermionic　emission　measurement　results　show　that　the　emission　current　density　of　the　single　crystal　is　47.1　A/cm(2)　at　1873　K　with　an　applied　voltage　of　1　kV,　which　is　about　two　times　larger　than　the　value　for　polycrystalline　samples.　The　single　crystal　possesses　excellent　emission　current　stability.　Therefore,　it　is　expected　that　CeB6　single　crystal　is　a　very　promising　material　for　thermionic　cathode　applications.