PURPOSE: To synthesize a high-purity aluminophosphate with excellent crystallinity in a short crystallization time by keeping a reaction mixture composed of a phosphoric acid source, alumina source and ethylpropylamine in a specific composition at a specified temperature.

CONSTITUTION: A phosphoric acid source is mixed with an alumina source, water and ethylpropylamine to prepare a reaction mixture having the following composition expressed in terms of molar ratios of oxides. 0.8-1.5 P2O5/Al2O3, 20-100 H2O/Al2O3 and 0.2-0.6 EPA/Al2O3 (EPA indicates C2H5NHC3H7). The resultant reaction mixture is then kept at 110-150°C temperature. Thereby, an aluminophosphate, substantially expressed by the formula Al2O3.1.0±0.2P2O5 based on an anhydrous state and having a powder X-ray diffraction pattern expressed by the table (W, M, S and VS respectively represent weak, medium, strong and very strong) in an uncalcined state is obtained by the above- mentioned method.