Photodegradation and demethylation reactions of methylene blue (MB) by a TiO2 photocatalytic film have been studied spectrophotometrically by estimating molar concentration changes of MB and demethylated species in an MB aqueous solution according to the Beer-Lambert law. On the other hand, MB was less demethylated by the reaction with an Au particles-TiO2 (Au-TiO2) composite film. (C) 2007 Elsevier B.V. All rights reserved.