This research aims to prepare unsaturated polyesters (UP) from polyethylene terephthalate waste (WPET) and studying their effects on the colloidal stability and dynamic mechanical properties of the prepared modified asphalt samples. To achieve this aim WPET is chemically recycled through glycolysis reaction using different glycols namely, diethylene glycol (DEG), triethylene glycol (TEG) and propylene glycol(PG) at molar ratios of PET wastes/glycol; 1:1.2 separately. The glycolyzed products were converted into unsaturated polyester (UP) via reaction with maleic anhydride. The prepared unsaturated polyesters (UPd, UPt and UPpg) were characterized using FTIR, GPC and TGA and then added to asphalt 60/70 in percentages ranging from 2wt% to 8wt% using wet process to prepare modified asphalt binder with desirable physical and engineering properties. The prepared modified asphalt samples were evaluated for thermal stability using TGA, physical and chemical properties using conventional tests, colloidal stability index while their rheological properties were investigated using Superpave binder tester, namely, dynamic shear rheometer (DSR) to determine the rutting and stiffness resistance of the prepared samples. The results showed an improvement in asphalt properties which became more thermally, colloidally stable and resistant to rutting and plastic deformation.