Sulfamic acid‐functionalized Fe3‐xTixO4 nanoparticles (Fe3‐xTixO4‐SO3H NPs) were fabricated as novel acidic magnetic nanocatalyst by the reaction of Fe3‐xTixO4 magnetic nanoparticles (MNPs) with 3‐chloropropyltrimethoxysilyl urea (TMSPU) followed by functionalization with chlorosulfonic acid. The structure of the synthesized nanocatalyst was studied using different methods including, Fourier‐transform infrared (FT‐IR), field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDX), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and dynamic light scattering (DLS). The potential catalytic ability of the synthesized MNPs was studied in one‐pot four‐component condensation reaction between aromatic aldehydes, dimedone, alkyl acetoacetates and ammonium acetate in order to synthesis of hexahydroquinoline derivatives. It was witnessed that the reactions proceeded smoothly under solvent‐free condition with high yields of corresponding hexahydroquinolines.