Tetra-valent cerium phosphate was synthesized from cerium oxide and phosphoric acid by heating. The sintering processes, pressure-less sintering (PLS), spark plasma sintering (SPS), and hydrothermal hot pressing (HHP), were tried to obtain polyphosphate bulks. Furthermore, the electrical conductivity of cerium polyphosphate bulks was investigated. Tetra-valent cerium phosphate was synthesized by heating at 700ºC for 20 hours. The hydrothermal hot pressing process was the suitable method to synthesize the tetra-valent cerium phosphate bulk. Y doped Ce(PO 3 ) 4 had higher conductivity than other rare earth phosphates. A part of tetra-valent cerium cation was considered to reduce tri-valent cerium cation and then to work as a dopant.