Erbium(III) selenate is an inorganic compound, with the chemical formula Er2(SeO4)3.

It exists as an anhydrate or an octahydrate.

Monoclinic erbium(III) selenate octahydrate can be crystallized from the solution when dissolving erbium oxide in selenic acid:[1] Erbium(III) selenate octahydrate is first dehydrated by heating to obtain the anhydrous form, and then heated continuously to obtain erbium selenite and finally erbium(III) oxide.

[1][2] It can crystallize with M2SeO4 in aqueous solution to form double salts, such as K3Er(SeO4)3·nH2O[3] and NH4Er(SeO4)2·3H2O,[4] etc.