This work presents a comprehensive synthesis method for the development of a new hyperbranched unsaturated polyester resin (HUPR). The resin is synthesized by modifying dehydrated castor oil fatty acid (DCOFA) with methyl methacrylate (MMA) and styrene, dicyclopentadiene-maleate (DCPD-M), and trimethylol propane diallyl ether (TMPDE). The synthesis process involves the radical addition reaction of DCOFA with MMA and styrene, followed by the addition of DCPD-M and TMPDE to form a HUPR. The resulting resin exhibits enhanced properties, making it a promising candidate for car body putty in the polymer industry.