Catalysts based on nanosized magnetic iron oxide stabilized inside the pore system of ordered mesoporous silica MCM-41 have been prepared. The obtained materials were characterized by powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and N-2 adsorption-desorption isotherm. XRD analysis showed that the obtained materials consist from the pure hematite crystalline phase (alpha-Fe2O3) dispersed within ordered mesoporous silica MCM-41. Magnetic measurements show that the obtained nanocomposites exhibit at room temperature weak ferromagnetic behavior with slender hysteresis. The catalytic activity of the magnetic alpha-Fe2O3/MCM-41 nanocomposites was evaluated by the degradation of methylene blue (MB) aqueous solution. For this purpose, an ultrasound-assisted Fenton-like process was used. The effect of solution pH on degradation of MB was investigated. The results indicated that US-H2O2-alpha-Fe2O3/MCM-41 nanocomposite system is effective for the degradation of MB, suggesting its great potential in removal of dyes from wastewater. It was found that the degradation rate of MB increases with decrease in the pH value of the solution. (C) 2012 Elsevier Inc. All rights reserved.