A series of Bi2O3-MgO composites were synthesized by solvent-thermal method. It was found that the Bi2O3-MgO composites perform much better than TiO2 (P25), Bi2O3 and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (lambda>400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi2O3-MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 degrees C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV-vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi2O3-MgO samples were also investigated. (C) 2010 Elsevier B.V. All rights reserved.