A dioxomolybdenum(VI) complex with the tridentate ONO Schiff base ligand was derived from the condensation reaction of 3-ethoxysalicylaldehyde with isonicotinohydrazide and then was immobilized on the surface of silica-coated magnetite nanoparticles. The resultant organic–inorganic hybrid material was characterized by infrared spectroscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscopy, vibrating sample magnetometry, and X-ray powder diffraction. The catalytic performance of the synthesized nanocatalyst was tested for the selective sulfoxidation of the different sulfides by using H2O2 as a safe oxidizing agent in ethanol as a green solvent under reflux conditions. The heterogeneous catalyst was recovered magnetically and reused at least five times without a notable decrease in its activity.