GeO2 single crystals with various morphologies were synthesized at room temperature by an acid-induced homogenous liquid phase precipitation technique without using any surfactants as studied previously. With addition of aqueous ammonia, the solubility of hexagonal GeO2 in water was significantly increased by formation of soluble germanate ions as confirmed by IR spectra analyses. Supersaturated GeO2 solution could be produced by adding acid into the GeO2-ammonia solution through the acid-induced transformation of germinate ions into GeO2. GeO2 spheres were obtained with phosphoric acid addition. Truncated cubic-like and cubic-like GeO2 single crystals could be produced in the solutions with hydrochloric acid and ascorbic acid (vitamin C) additions, respectively. The morphology developments of the GeO2 particles induced by various acids were discussed and the growth mechanism conforms to BFDH and HP crystal growth models. (C) 2007 Elsevier B.V. All rights reserved.