Ammonium selenate is a chemical compound with the chemical formula (NH4)2O4Se.

[1][2] Synthesis is via a reaction of selenic acid with an excess of ammonium hydroxide.

[3] It may also be formed by the effect of an ammonia solution on a solution of selenic acid: Ammonium selenate forms white crystals of monoclinic system, spatial group C2/m, cell parameters a = 12.152, b = 6.418, c = 7.711, β = 115.5° Z = 4 and density 2.190 Mgm−3.

[4] It is easily soluble in water.

[5] Soluble in EtOH and acetone.