Magnetite nanoparticles were used as a core for –OSO₃H functionalized mesoporous MCM-41 shell to provide a core–shell solid acid catalyst (Fe₃O₄@MCM-41-OSO₃H). The catalyst was characterized by transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and a vibrating sample magnetometer (VSM). The obtained nano-magnetic catalyst was used in the three-component reaction of indoles, aldehydes and thiols to furnish the desired 3-[(aryl)(arylthio)methyl]-1H-indoles in good yields under very mild reaction conditions. The unique feature of the reaction was the ease of work-up and catalyst recovery. The recovered catalyst maintained catalytic activity for five successive runs.