Yttrium(III) hydroxide is an inorganic compound and an alkali with the chemical formula Y(OH)3.

Yttrium(III) hydroxide can be produced by reacting yttrium(III) nitrate and sodium hydroxide in aqueous solution:[1] This gives yttrium(III) hydroxide as a white gelatinous precipitate, which can be dried to a white powder.

[2] Yttrium(III) hydroxide is an alkali, so it can react with acid: The compound absorbs atmospheric carbon dioxide.

[2] When heated, yttrium(III) hydroxide will decompose: