A alpha-/gamma-Bi2O3 composite has been successfully prepared via a hydrothermal method. The as-prepared nanocrystals are characterized by the X-ray diffraction, Fourier transformation infrared spectrum, Scanning electron microscopy, Transmission electron microscopy, and high-resolution transmission electron microscopy examination. The homojunction between the alpha-Bi2O3 and gamma-Bi2O3 is confirmed by the diffuse reflectance spectra and impedance spectrum. The photocatalytic activities of the samples were evaluated by the degradation of Rhodamine B as a model pollutant. The composite exhibited higher photocatalytic activity than bare alpha-Bi2O3 or gamma-Bi2O3 in the degradation of RhB. The enhanced photocatalytic activity is attributed to the synergetic effect of the homojunction. (C) 2012 Elsevier B.V. All rights reserved.