PURPOSE: To inexpensively obtain a high purity AlPO4 powder having a desired P2O5/Al2O3 molar ratio useful as a sintering assistant, an adhesive and a chemical synthesizing catalyst by dissolving a metallic Al in a phosphoric acid, precipitating a hydrous AlPO4 by adjusting pH, and drying and calcining the hydrous AlPO4 thus obtained.

CONSTITUTION: (A) As to 99.99wt.% purity industrial Al, its ≤80% quantity is dissolved preferably in (B) an electronic industrial purity phosphoric acid more than its 3 times equivalent to Al, so that the concentration becomes ≥20wt.% with heating at 40W80°C at need, and an insoluble metallic Al is removed. Subsequently this solution is diluted so that the Al concn. goes down to ≤20g/l and the PO4 group concn. down to ≤200g/l, the pH is adjusted within 3.3W3.8 by adding an aq. ammonia, etc., then the AlPO4 is deposited, precipitated, separated through a filtration and washed with water. The hydrous AlPO4 thus separated and washed is dehydrated by heating up to, e.g. about 300°C, furthermore is calcined at ≥300°C preferably ≥1,000°C.