Polycrystalline　hexaborides　(LaxGd1-x)B-6　(x　=　0,　0.6,　0.8,　1)　were　synthesized　by　the　reactive　spark　plasma　sintering　(SPS)　method　using　a　mixed　powder　of　LaH2,　GdH2　and　B.　The　effects　of　La　doping　contents　on　the　crystal　structure,　grain　orientation,　electrical　resistivity　and　thermionic　emission　properties　were　investigated　by　x-ray　diffraction,　electron　backscattered　diffraction　and　emission　current　measurements,　respectively.　The　results　indicate　that　the　high-purity　(LaxGd1-x)B-6　cathode　sintered　by　SPS　exhibits　high　densification　(＞　97%)　and　a　high　value　of　the　Vickers　hardness　(2375　kg　mm(-2)).　When　the　La　doping　contents　are　increased,　the　thermionic　emission　current　density　increases　from　11.00　to　36.20　A　cm(-2).　Thus,　the　SPS　technique　is　a　suitable　method　for　synthesizing　dense　rare-earth　hexaborides　with　excellent　properties.