Ferrite bismuth nanoparticles as a visible light photocatalyst were successfully synthesized via ultrasound. The optimum conditions were found and applied for the sono-synthesis of the catalyst. The product was characterized by different methods. The nanoparticles were used for the degradation of methylene blue as a typical dye pollutant. In acidic medium, the photocatalytic degradation was carried out under direct sunlight irradiation. In basic medium, without catalyst, the methylene blue was degraded through photolysis under sunlight irradiation. The effect of parameters such as the amount of catalyst and initial concentration of the dye was investigated on the removal efficiency of methylene blue. The adsorption isotherm and the kinetic of photocatalytic degradation were studied under different conditions. Furthermore, the degradation efficiency and the chemical oxygen demand reduction were 100% and 83% for the photocatalytic process, respectively. (c) 2013 Elsevier B.V. All rights reserved.