PURPOSE: To obtain a maleinized resin of superior heat resistance and higher reactivity, by reacting a polycyclic aromatic polymer component contained in a residue from the thermal-cracking of naptha with maleic anhydride.

CONSTITUTION: A polycyclic aromatic polymer component having a n-hexane- insoluble content ≥80wt.%, which is part of a residue from the thermal # cracking of naphtha, is reacted with maleic anhydride to form a maleinized resin. When a maleinized resin remarkably improved in heat resistance is desired, a polycyclic aromatic polymer component having said n-heptane-insoluble content ≥80wt.% and a bottom obtained from distillation operated at a bottom temperature of 100W550°C are reacted with maleic anhydride. Said maleinization is usually carried out at about 50W400°C in the presence of a catalyst and a solvent.