Abstract: Fatigue and rutting phenomena are major distresses in asphalt pavements. Asphalt mixture properties are highly dependent upon the asphalt binder and the mastic behavior. The purpose of this study was to investigate the behavior of the asphalt binder and the mastic, modified by the synthesized polyurethane, at high and intermediate temperatures. The filler/asphalt binder ratio (by weight) was 1.0. The dynamic shear rheometer (DSR) was used to measure fatigue (G*sin δ) and rutting (G*/sin δ) parameters. In this study, the multiple stress creep and recovery (MSCR) test was also utilized to calculate the rutting potential of the asphalt binder and the mastic. Parameters of the non-recoverable compliance (J_nr) and the percentage recovery (%) were evaluated at high temperatures. The obtained results indicated that the synthesized polyurethane improved the rutting and fatigue properties. There was a significant correlation between the asphalt binder and the mastic in terms of the complex modulus (R² = 0.9958), rutting (R² = 0.9944), and the non-recoverable compliance (R² = 0.9707). For the fatigue parameter (R² = 0.9852), the complex modulus (R² = 0.9855), and the phase angle (R² = 0.8262), significant relationships were observed between the asphalt binder and mastic samples at intermediate temperatures. Overall, the chemical reaction between the filler and the asphalt binder could be effective in different behaviors of the mastic and asphalt binder. There was a 112%–164% increase in the G*sin δ parameter for mastics, compared to that of the asphalt binder. The complex modulus was 6 times higher by adding the filler content.