We have successfully prepared transparent anatase nanocomposite films on various types of substrates, including organic polymers, using the sol-gel method at temperatures <100 degrees C under ambient pressure. This novel process is based on the findings that (i) anatase nanocrystals are uniquely formed in sol-gel-derived SiO2-TiO2 films that have been subjected to a hot-water treatment, and (ii) the addition of an organic polymer such as poly(ethylene glycol) in the films accelerates the formation of anatase nanocrystals. The film coating on the substrates is a promising candidate for use as a photocatalyst to decompose environmental pollutants and harmful microorganisms.