A novel sonochemical approach was developed for the synthesis of different core/shell structures of Fe₃O₄/SiO₂/Ag nanocubes and SiO₂/Ag nanospheres. The total reaction time of the three sonochemical steps for the synthesis of Fe₃O₄/SiO₂/Ag nanocubes is shorter than that of the previously reported methods. A proposed reaction mechanism for the sonochemical functionalization of the silica and the silver on the surface of magnetic nanocubes was discussed in detail. Transmission electron microscopy revealed that the surface of Fe₃O₄/SiO₂ nanocubes was decorated with small Ag nanoparticles of approximately 10–20 nm in size, and the energy dispersive spectroscopy mapping analysis confirmed the morphology of the structure. Additionally, X-ray diffraction data were used to confirm the formation of both phases of a cubic inverse spinel structure for Fe₃O₄ and bcc structures for Ag in the core/shell structure of the Fe₃O₄/SiO₂/Ag nanocubes. The as-synthesized Fe₃O₄/SiO₂/Ag nanocubes showed a high efficiency in the catalytic reduction reaction of 4-nitroaniline to 4-phenylenediamine and a better performance than both Ag and SiO₂/Ag nanoparticles. The grafted silver catalyst was recycled and reused at least fifteen times without a significant loss of catalytic efficiency.