Basic copper or magnesium carbonate was mixed with phosphoric acid in the mole ratio of P/M=2 (M; Cu or Mg). Each mixture was transformed to cyclo-tetraphosphate by heating. A part of the basic copper or magnesium carbonate was replaced with a rare earth oxide (La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Yb₂O₃, and Y₂O₃) in this system. These mixtures containing one of the rare earth oxides were heated and then the products were analyzed by XRD, FT-IR, and TG-DTA. It was observed in copper system that the product changed from cyclo-tetraphosphate to pyrophosphate by the addition of rare earth oxide used in this study. In magnesium system, magnesium cyclo-tetraphosphate was formed in spite of the addition of rare earth oxide. Surface properties, specific surface area, acid strength and amount of acid sites, catalytic activity for dehydration of 2-propanol and cracking / dehydrogenation of cumene, were measured to clarify the role of rare earth element in magnesium cyclo-tetraphosphate.