In this study, the change in the physical, chemical, microstructural, and rheological properties of a road bitumen modified with reactive terpolymer (ElvaloyA (R) RET) was investigated. For this purpose, four different ElvaloyA (R) RET percentages (0%, 0.4%, 0.8%, and 1.2% by wt.) were mixed with B 160/220 bitumen. Firstly, the obtained samples were subjected to a short and long-term aging process using a rotating thin-film oven test and pressurized aging vessel, respectively. Then, the engineering characteristics of the samples were investigated using X-ray diffraction, scanning electron microscopy, and conventional and Superpave bitumen tests. The results showed that ElvaloyA (R) RET reacted with the main macromolecular groups in the bitumen, and that the modified bitumens behaved as a homogenous single phase structure as a result of this reaction. Conventional tests showed that ElvaloyA (R) RET-modified bitumens were much harder than pure bitumen and had better aging resistance. Furthermore, the penetration classes of these bitumens changed and their temperature sensitivities decreased significantly. Rheological tests showed that the ElvaloyA (R) RET additive increased the resistance of the bitumen against fatigue cracking and particularly permanent deformation. Moreover, the high temperature performance class of the bitumen also increased. However, parallel to the hardening of the bitumen, a reduction in its resistance to cracking at low temperature was observed.