It is used as a molybdenum source in fertilizers analytical reagent for phosphate detection (molybdophosphoric blue complex) catalyst precursor in petroleum refining and in pigmentcorrosion inhibitor production.

Its primary purpose is forming heteropoly acids with phosphates for sensitive colorimetric assays at 690880 nm while providing bioavailable Mo for plant nutrition and enzyme cofactors.

Ammonium molybdate tetrahydrate is a white to yellowish crystalline powder also called ammonium heptamolybdate tetrahydrate with molecular weight 1235.86 gmol density 2.50 gcm decomposition starting around 90C with ammonia release and good water solubility (43 g100 mL cold).