In this study, photocatalytic degradation of rhodamine B dye has been investigated as an efficient method to remove this contaminant from aqueous solutions [2,1]. In this regard, using green synthesis as one of the cleanest methods to produce metal oxides, a magnetic composite of tin oxide was prepared for use as a photocatalyst [3]. The specifications of synthesized composite were then determined by common methods [4]. The results of characterizing the prepared composite as a photocatalyst showed that the synthesized structure has an average particle size of 22.5 nm, surface charge + 38 mV and a magnetic property of 20 emu/g. In addition, in order to achieve the maximum photodegradation efficiency (PDE), the effect of important factors such as pH, amount of photocatalyst, initial dye concentration, plus the presence of oxidizing H2O2 and Fe2+ ion was investigated and optimized. Effective on the process, pH = 5.5, dye concentration of 52.5 mg/L, and value of 0.75 g/L of the magnetic nanocomposite were determined as the best operating conditions, degradation efficiency was 83.4%. The results of the study of the effect of Fentoni agents showed that the addition of concentrations of 200 mg/L of hydrogen peroxide and 3.5 mg/L of ferrous ions resulted in 100% dye degradation only 45 min after the start of the process
