Germanium(II) hydroxide, normally written as Ge(OH)<sub>2</sub>, is a poorly characterised compound, sometimes called hydrous germanium(II) oxide or germanous hydroxide. It was first reported by Winkler in 1886.
Germanium(II) hydroxide is formed as a white or yellow precipitate when base is added to solutions containing Ge<sup>II</sup>, produced for example by the reduction of an acid solution of germanium dioxide, GeO<sub>2</sub>, with hypophosphorous acid, H<sub>3</sub>PO<sub>2</sub>, or alternatively by hydrolysis of GeCl<sub>2</sub>. The initial precipitate, which has no definite stoichiometry, can be represented by GeO÷xH<sub>2</sub>O, Ge(OH)<sub>2</sub>÷xH<sub>2</sub>O, or loosely Ge(OH)<sub>2</sub>. It is only slightly soluble in water or alkali and not appreciably soluble in perchloric acid, HClO<sub>4</sub>, but is soluble in hydrochloric acid, HCl. On digestion with sodium hydroxide, NaOH, it yields a brown insoluble compound, which after drying in vacuo forms a brown pyrophoric substance with the approximate stoichiometry of (HGe)<sub>2</sub>O<sub>3</sub>. On the basis of the infrared spectrum, (HGe)<sub>2</sub>O<sub>3</sub> may contain a germanium hydrogen bond, Ge-H.