Polyaniline (PANI) modified TiO2 nanocomposites were successfully synthesized via an 'in situ' oxidative polymerization method. The modified nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectra, thermogravimetric analysis, cyclic voltammetry, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic degradation of methylene blue was chosen as a model reaction to evaluate the photocatalytic activities of TiO2 and PANI/TiO2. The results indicated that PANI/TiO2 nanocomposites exhibited good photocatalytic activity (apparent first-order rate constants of 0.0021 min(-1) for TiO2 and 0.0051 min(-1) for P/T(1/5)) and stability (recycled 5 times, 15 hours of operation). The photocatalytic activity of PANI/TiO2 increased as the initial pH increased because of electrostatic adsorption between the photocatalyst and MB as well as the generation of center dot OH, whereas it exhibited an earlier increasing (from 0.5 g/L to 1.0 g/L) and later decreasing (from 1.0 g/L to 2.0 g/L) trend as the concentration of the photocatalyst increased owing to the absorption of visible light. The photocatalytic stability of the PANI/TiO2 nanocomposite was dependent on the stability of its structure. The possible photocatalytic mechanism and photocatalytic activity enhanced mechanism has been proposed, taking into account the photosensitization effect and synergetic effect of TiO2 with PANI. (C) 2017 Elsevier Ltd. All rights reserved.