Poly(1-vinylimidazole) reacts with silicic acid and poly(silicie acid), giving rise to water-soluble complexes and insoluble composites because of hydrogen bonding. The composition, structure, and morphology of the obtained products have been studied with elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The main direction of the reaction depends not only on the initial ratio of the components, concentration, and pH but also on the sequence of the reagent mixing: the presence of poly(1-vinylimidazole) macromolecules during the Formation of silicic acid stabilizes soluble complexes, which precipitate with an excess of H4SiO4 only. These soluble complexes may serve as a pattern of particles responsible for the transport of silicic acid in diatom algae and other organisms that assimilate silicon from the environment. (c) 2005 Wiley Periodicals, Inc.