Abstarct: This thesis experimentally and analytically investigates the mechanical performance of asphalt mixtures modified with recycled crumb rubber (CR) and steel slag (S) under varying temperature conditions. The evaluation was conducted using three tests: Indirect Tensile Strength (IDT), Kim Test (KIM) for rutting/deformation resistance, and Semi-Circular Bend (SCB) for low-temperature fracture behavior, on nine mix designs including CTRL, 5CR, 10CR, 5S, 10S, and hybrid CR–S combinations. IDT results at 20, 30, and 40°C showed that steel slag consistently increased tensile strength (ITS), with 5S performing best at 20 and 30°C and 10S at 40°C. In contrast, CR generally reduced ITS, which is attributed to increased mixture ductility. ITS decreased with increasing temperature for all mixtures; however, slag-modified mixtures exhibited the lowest temperature sensitivity. A second-order regression model with high accuracy (R² = 0.952). KIM test results at 40 and 60°C indicated that steel slag improved deformation resistance, with 5S achieving the highest stability (SD) at 40°C. At 60°C, however, the CTRL mixture performed best, suggesting that binder softening dominates at very high temperatures. CR generally reduced SD, while hybrid mixtures showed intermediate behavior; notably, 5CR5S exhibited the most stable performance across both temperatures. A regression model for SD was also developed with good agreement (R² = 0.909). SCB testing at 5, 10, 15, and 20°C demonstrated that hybrid CR–S mixtures provided the best overall fracture performance. At 5°C, performance depended on the index: 5S showed the highest Flexibility Index (FI), while 5CR5S achieved the highest values of CRI, CTI, and fracture energy (Gf). At 10 and 15°C, 5CR10S consistently exhibited superior overall performance, leading in FI and CTI and recording the highest Gf. At 20°C, this mixture remained superior in FI, CRI, and CTI, while 10CR10S showed the highest Gf. Collectively, steel slag enhanced stiffness and crack resistance, whereas crumb rubber improved ductility and post-peak energy dissipation. Their combination—particularly 5CR10S—provided the most stable performance across the studied temperature range. The developed predictive model for fracture indices also showed acceptable agreement with experimental results (R² = 0.749).