BiFeO3 nanoparticles with controlled particle size were synthesized via sol-gel method. The samples were characterized by X-ray powder diffraction, transmission electron microscope, Raman spectra, nitrogen adsorption technique and UV-vis diffuse reflectance spectra. Photocatalytic activity of BiFeO3 nanoparticles was further examined by monitoring the degradation of Rhodamine B dye in an aqueous solution under visible light irradiation. Through the calculation of band position and a number of diagnostic experiments, the photocatalytic mechanism of BiFeO3 nanoparticles was proposed in this study. It was found that the hydroxyl radicals originated from the photogenerated electrons were the main reactive species responsible for the pollutant degradation. Moreover, with the variations of annealing temperature and time, the average crystallite size, specific surface area and crystallinity of BiFeO3 nanoparticles could be changed, which thus affected the photocatalytic activity of the corresponding samples. (C) 2013 Elsevier Ltd. All rights reserved.