Abstract: In this paper we have studied the reaction between the aqueous solution of P₂O₇^4- and Ce ( Ⅳ ) obtained by chemical oxidation of the corresponding trivalent species in an alkaline aqueous pyrophosphatc solution using ozonc. under different conditions three solids of Ce P₂O₇·x H₂O, K₂(Ce(HP₂O₇ )₂)·4H₂Oand K₄(Ce(P₂O₇)₃)·3H₂Owere obtained from the solution of Ce( Ⅳ)-P₂₇^4- with different methods. The compositions and the properties of these solids were studied by chemical analysis, thermal analysis, infra-red spectrum and the determination of molar conductivities and charges of the complex ion.