A simple electrostatic self-assembly method was developed to uniformly disperse ultra-fine Au nanoparticles (NPs) on TiO2 film to improve the photocatalytic activity. Without any modification of TiO2 surface with functional groups, negatively charged Au NPs could be spontaneously adsorbed on TiO2 films with electrostatic attraction when the pH of Au colloids was lower than or close to the isoelectric point of TiO2. Ultra high-resolution FESEM observation showed that Au NPs with diameter of 3-5 nm were physically separated and uniformly dispersed on TiO2 film. The pH of Au colloids remarkably influenced the Au loading that was decreased at high pH. The average size of deposited Au NPs increased from 3.1 +/- 13 nm at -5 degrees C to 10.5 +/- 3.1 nm at 40 degrees C. indicating that growth of Au NPs was retarded at low temperature. The dispersed Au NPs on TiO2 film enhanced the photocurrent generation with five folds and increased the photovoltage of similar to 115 mV, revealing that the recombination of electron-hole pairs was significantly reduced. The photocatalytic activity of the Au-TiO2 nanocomposite film was improved with similar to 2.5 folds for degradation of bisphenol A, and no deactivation was observed during 10 cyclic tests. The key characteristics of deposited Au NPs, such as ultra-fine size, uniform dispersion, physical separation and high loading, were responsible for improved photocatalytic activity of the Au-TiO2 film. (c) 2009 Elsevier B.V. All rights reserved.