The new potassium cerium(III) phosphate of formula K4Ce2P4O15 in the system Ce2O3-K2O-P2O5 was prepared by solid state reactions and characterized by thermal analysis (DTA, TG, DSC), powder X-ray diffraction and IR spectroscopy. This compound exists only in the solid state (below 880degreesC) and exhibits a polymorphic transition at 527 degreesC. The low-temperature form beta-K4Ce2P4O15 of this compound crystallizes as a triclinic phase (space group P) with unit cell parameters: a = 9.319(7), b = 12.129(3), C = 9.252(1)Angstrom,alpha = 106.875, beta = 100.086, gamma = 107.202degrees. V = 916.276 Angstrom(3). (C) 2004 Elsevier B.V. All rights reserved.