Enzymes are an important class of biological molecules whose specific functionalities can be exploited to perform tasks beyond the reach of conventional chemistry. Because they are operational under environmentally friendly, ambient conditions, the adaptation of these biomacromolecules can potentially be used to replace current energy-intensive and environmentally harsh synthesis methods for materials. Here we used a hydrolytic enzyme, urease, to modify the solution environment around a water-soluble and stable TiO2 precursor to synthesize nanocrystalline titanium dioxide under environmentally benign conditions. This ureasemediated synthesis yields nearly monodisperse TiO2 nanostructures with high surface area that can be utilized for numerous energy-based applications such as low-cost photovoltaics and photocatalysts.