AbstractOver the last 20 years, many polymer-based additives have been used in asphalt modification. The extensive utilization of these additives and their inability to biodegrade create environmental concern for humans. Therefore, discovering affordable and naturally occurring asphalt polymers has become prominent. In this study, a new asphalt modifier was produced under laboratory conditions by synthesizing boron oxide with rosin (colophony resin), which is naturally produced from pine trees. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC)/thermogravimetric (TG), and X-ray powder diffraction (XRD) analyses were used to determine the microstructural characteristics of the produced modifier. The SEM analysis showed that the new modifier was distributed homogeneously the asphalt matrix, the FTIR and XRD analyses showed that a chemical synthesis had taken place, while the DSC and TG analyses determined the thermal structure characterization and temperature range of the modifier. The rheological properties of the modified asphalts were investigated by conducting penetration, softening point, ductility, flash point test, rotational viscosity (RV), and dynamic shear rheometer (DSR) tests. The results showed that the new modifier could be produced in a laboratory environment, the temperature sensitivity of the original asphalt was reduced by 48% with a 3% additive rate, and the modified asphalt provides a wide range of usage in hot climates. Conclusively, the boron-added resin compound (BARC) additive did not adversely affect the workability and pumpability properties and the BARC-modified asphalt binders significantly increased the rutting resistance.