The single perovskite BiFeO3 nanoparticles were prepared by a sol-gel process. The BiFeO3 nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy, and Brunauer-Emmett-Teller (BET) method. It was found that the prepared BiFeO3 nanoparticles show the large specific surface area of 136 m2/g, and narrow band gap of 2.12 eV. Consequently, BiFeO3 nanoparticles show high visible-light photocatalytic activity for decomposition of methylene blue in comparison with the commercial Degussa P25. It is concluded that the large specific surface area and the narrow band gap contribute to the high visible-light photocatalytic activity through enhanced adsorption capability and visible-light absorption.