Ammonium phosphomolybdate is the inorganic salt of phosphomolybdic acid with the chemical formula (NH4)3PMo12O40.

The salt contains the phosphomolybdate anion, a well known heteropolymetalate of the Keggin structural class.

Ammonium phosphomolybdate can be made by heating ammonium orthomolybdate combined with phosphoric acid and nitric acid, yielding ammonium nitrate, water, and a yellow precipitate of ammonium phosphomolybdate is obtained.

[3] Normally, it often exists as a hexahydrate, a dark yellow fine crystal which is poorly soluble in water.

[3] It is also obtained as a test result for phosphate ions.