The present work focuses on the ability of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBOMA) and methyl methacrylate (MMA) as reactive diluents to replace styrene in unsaturated polyester resin based on itaconic acid, sebacic acid, 1,4-Butanediol, 1,6-Hexanediol and glycerol. The structural analysis confirmed the presence of itaconate linkages in the UPs. The synthesized resins were characterized by infrared spectroscopy and their physiochemical properties such as appearance, viscosity, acid value, %volatile content, curing characteristics like gel time, peak exotherm temperature and total cure time. Among all the resins formed; the resin based on 1,6-Hexanediol showed optimum molecular weight and viscosity needed for final application. The cured resins were investigated for their thermal stability by thermo-gravimetric analysis which revealed that all the diluted resins had good thermal stability. From the results it could be concluded that styrene-free bio-based unsaturated polyester resin can be synthesized having properties equivalent to the commercial styrene based resin.GRAPHICAL ABSTRACT