Polycrystalline rare-earth hexaboride (LaxCe1-x)B6 were prepared by means of the reactive spark plasma sintering (SPS), using mixed powders of GdH2, NdH2 and B. The crystal structure, surface texture, mechanical property, electrical resistivity, and thermionic emission properties of the sintered samples were investigated. It is found that all the samples sintered by SPS exhibit high densily (>96%) and high value of Vickers hardness (2310 kg/mm2), which are much higher than those made by traditional method. Thermionic emission results indicate that the maximum emission current density of La0.6Ce0.4B6 is 40.7 A/cm2 under the applied voltage of 1 kV at 1873 K, which is larger than that of LaB6 and CeB6. Thus, the mixed cystal of borides (LaxCe1-x)B6, as a cathode, promises good prospects in application.