In the present study, for the first time the synthesis of organic-inorganic MCM-41 mesoporous magnetite nanoparticles (MNPs@MCM-41) as a new class of solid acid catalyst with large density of sulfonic acid groups was suggested. The specific surface area and textural property of synthesized nanoparticles were improved through the coupling of inorganic and organic components by template synthesis on the magnetite nanoparticle surface. The new solid acid catalyst was prepared in three steps: (i) preparation of colloidal iron oxide magnetite nanoparticles (Fe3O4-MNPs) with particle size lower than 8.0 nm, (ii) development of an organic-inorganic MCM-41 mesoporous structure with thiol groups on the surface of MNPs (Fe3O4@MCM-41-SH) and (iii) oxidation of thiol groups to sulfonic acid (Fe3O4@MCM-41-SO3H). The incorporation of sulfonic acid as a functional group on the surface of MNPs@MCM-41 was achieved by simultaneous reaction of condensable inorganic silica species and thionilayted organic compounds (co-condensation, one-pot synthesis) that lead to magnetite mesoporous solid acid catalyst. The properties of prepared magnetite nanocomposite were characterized by FT-IR, XRD, UV-DRS, TEM, VSM and titration. Finally, the applicability of the synthesized nanocomposites was tested as heterogeneous solid acid catalyst for one-pot three component synthesis of aryl benzo[alpha]xanthenone derivatives in room temperature and solvent free conditions. (c) 2013 Elsevier B.V. All rights reserved.