Oxidative polymerization of pyrrole is initiated by photoexcited TiO2 nanoparticles. Pyrrole oligomers rend polypyrrole (PPy) are continuously produced with reaction time. The conversion of pyrrole monomer changes as a function of the concentration of TiO2 nanoparticles. It is found that PPy in the composite has the conjugated structure and is partially oxidized with a formation of positively charged N+. Results from X-ray photoelectron spectroscopy and Raman analysis consistently indicate that a strong interaction is esiablished between the TiO2 and PPy. According to the results of UV-vis spectroscopy, a mechanism of photocatalytic oxidation is proposed for this polymerization. The interaction between TiO2 and PPy is found to arise from the photocatalytic reaction and discussed in terms of photoinduced Ti3+. (C) 2008 Wiley Periodicals, Inc.