Copper slag (CS) is an abrasive blasting grit made of granulated slag from metal smelting processes. As copper slags are known to be waste material and cause a lot of environmental problems, it would be a good idea to use them in different sections of industry such as pavement construction. On the other hand, in order to save energy and reduce the amount of pollutants released during the construction of asphalt pavements, the technology of Warm Mix Asphalt (WMA) is developing considerably. A very high amount of copper slag is produced in south of Iran where the weather is considered to be hot and rutting is the most important distress of asphalt concretes. This paper presents the influence of utilization of copper slag as fine material on the rutting performance of warm mixed asphalt. A laboratory study has been conducted on five asphalt mixtures with various CS contents, namely; 0%, 10%, 20%, 30% and 40% by weight of total aggregates. The amount of optimum bitumen and the value of Marshall Stability (MS) were determined with MS test for the samples. Then creep test and wheel track tests were conducted on the produced samples. The results indicated that the use of 20% CS in WMA enhances the marshal stability and rutting performance of WMA mixtures. However, the resistance of mixtures against rutting falls substantially by adding more than 20% CS.