A transparent, high purity, amorphous titanium dioxide thin film composed of densely packed nanometer-sized grains has been successfully deposited on a glass substrate at room temperature from an aqueous peroxotitanate solution using a simple, inexpensive, reproducible, and environmentally friendly method. The as-deposited thin film was 117 nm thick and composed of closely packed particles of 10–15 nm in diameter, but they aggregated into large grains of 50–100 nm in diameter. The aqueous peroxotitanate solution was obtained by dissolving metatitanic acid (H₂TiO₃) in a mixture of concentrated H₂O₂ and NH₃·H₂O. An anatase TiO₂ thin film was obtained by heating the as-deposited thin film at 500 °C for 1 h in air. A chemical composition of TiO_1.4(O₂)_0.5(OH)_0.2·1.34H₂O is proposed for the as-deposited thin film, based on XPS, FT-IR and TG-DTA data. Band gap energies of 3.20 eV for indirect transition and 3.63 eV for direct transition were obtained for the anatase TiO₂ film.