Abstract: In this study, a magnetic nanocomposite based on poly (styrene-co-maleic anhydride) (Fe3O4 @ PSMASA) was prepared in three steps. In the first step, poly (styrene-co-maleic anhydride) was prepared from the radical polymerization reaction of styrene and maleic anhydride monomers. In the second step, the iron oxide magnetic nanoparticles prepared by co-precipitation method were functionalized using 3-aminopropyltriethoxycylan (APTES). In the third step, the maleic anhydride ring in the copolymer was modified with sulfanilic acid and amine-activated magnetic iron nanoparticles to form carboxylic acid and sulfonic acid groups on poly (styrene-co-maleic anhydride). The catalytic activity of the resulted Fe3O4 @ PSMASA was investigated in the three-component reaction of isatoic anhydride, amines and aldehydes in ethanol as solvent. This method led to the synthesis of various derivatives of 3,2-dihydroquinazoline-4 (1H) in high yields. The catalyst can be recovered and reused in the reaction without significant loss catalytic activity. The other advantages of this method include high efficiencies, mild reaction conditions, good performance and environmental friendliness.