A novel recyclable magnetic core–shell nanoparticles Fe3O4@saponin/Cd was synthesized by the combination of nano-Fe3O4@saponin with cadmium acetate. The structure, magnetic features, and morphology of magnetic nanoparticles (MNPs) Fe3O4@saponin/Cd were studied totally via different experiments, such as Fourier transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), inductively coupled plasma (ICP), high-resolution transmission electron microscopy (HR-TEM), and Brunauer–Emmett–Teller (BET). It was found that the catalyst was active for the synthesis of β-aminoketone derivatives via one-pot three-component Mannich-type reactions of ketones, aromatic aldehydes, aromatic amines under eco-friendly solvent, at room temperature. Furthermore, this catalyst can be easily recovered magnetically and can be reused for other runs without any reduction in the activity.