In this work, we prepare the TiO2 nanoparticle film and anatase TiO2 nanoarray film, and we achieve the polymerizations of thiophene using the photoexcited TiO2 film as the initiators. It is measured that the in situ polymerizations of thiophene take place on the surfaces of the two films. The growth of polythiophene (PTh) on the TiO2 nanoarray is monitored using Fourier-transform Raman spectroscopy. The TiO2 nanoarray is found to strongly interact with the PTh polymers. It is observed using scanning electron microscope that the microspores in the nanoarray are filled by the polymers after the reaction of 3 h, and the nanoarray is fully covered by the polymer layer when the polymerization lasts for 5 h. The PTh–TiO2 nanoarray composite films are measured for the transient photocurrents and photocurrent-voltage characteristics. The dependence of the photocurrents on the reaction time is revealed and discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40187.