1-Methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles ([HSO₃PMIM]OTf–SiO₂@MNPs) was prepared by immobilization of [HSO₃PMIM]OTf onto the surface of silica-coated Fe₃O₄ nanoparticles and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and FT-IR techniques. Efficient synthesis of mono- and bis-isobenzofuran-1(3H)-ones was performed in the presence of this catalyst under thermal conditions and MW irradiation. The catalyst could be easily separated by an external magnet and reused six times under thermal conditions and MW irradiation without significant loss of its activity.