Sustainable development, has drawn so much attention in recent decades. Considering depletion of fossil fuel resources, and also environmental issues caused by air pollution, it seems necessary to reduce the temperature demand in producing asphalt mixtures. At the same time, the increasing number of construction projects, and the limited amount of mineral aggregates, highlight the fact that mineral aggregates should be replaced by some secondary materials. Using recycled and secondary materials has many benefits, such as preserving non-renewable resources, decreasing environmental pollution, and regaining energies consumed in production of such materials. In order to reduce the pollution and to protect the environment some strategies can be implemented when manufacturing asphalt mixtures. Some of such strategies are reducing the temperature demand in production and compaction of asphalt mixtures, replacing mineral aggregates with secondary materials, utilizing different technologies to improve load carrying capacity, which in turn leads to a thinner asphalt layer. Steel slag is a by-product of steel manufacturing process and is considered as a waste material and also a pollutant element for the environment. Natural aggregates of asphalt mixtures can be substituted by steel slag due to its unique qualities. Although many studies have been conducted about warm asphalt technology in different parts of the world, the long-term performance of warm mix asphalt is still remained as one of the ambiguities of this technology. Hence, in this study, the long-term performance of warm asphalt mixtures containing steel slag is investigated. The asphalt used in the present research is PG 64-22 with 60-70 penetration grade and the aggregates are made of limestone and Electric Arc Furnace steel slag. Sasobit has also been used as an additive in manufacturing warm asphalt. Due to the use of 1.5 percent sasobit, mix and compact temperature of asphalt mixtures is decreased by 20 °C. Furthermore, in order to simulate the short-term and long-term aging, asphalt samples were put in the oven with specific temperature and for particular times based on AASHTO standard. Sasobit is mixed with asphalt by conventional mixer and high shear mixer. Traditional and SHRP tests conducted on mixtures indicated that sasobit is insensitive to mixing conditions. Performance of asphalt samples were evaluated by Marshall stability test, resilient modulus test at 25°C and 40°C, indirect tensile strength test, moisture susceptibility test and dynamic creep test. Finally, the ratio between the results of long-term and short-term aging of one parameter is introduced as aging ratio. Aging ratio of mixtures containing steel slag is increased compared to mixtures made with limestone aggregates. Likewise, the aging ratio of hot mixtures is more than that of warm mixtures. In general, aging leads to a reduction in indirect tensile strength and moisture resistance of asphalt mixtures. Moreover, aging causes the Marshall stability, Marshall quotient, resilient modulus and rutting strength to increase in asphalt mixtures. Obviously, this increase does not mean that aging will enhance the performance. In fact, the main reason of this improved performance is the increase in stiffness of mixtures. Hardening of asphalt mixtures due to aging, results in a more brittle behavior. Increased brittleness, along with reduced adhesion between asphalt pavement and material, undermines the fatigue performance of the mixture and leads to formation of early cracks in the aged asphalt mixtures. Keywords: Warm mix asphalt, steel slag, sasobit, aging