Ionic liquids (IL), are reported to be new environmentally friendly solvents. Due to their unique properties and wide diversity, IL's can be used as surfactants to recover oil from mature fields. However, despite their promising performance, studies have revealed that IL are not environmentally friendly as claimed. In this paper, a brief review of the literature was conducted, including main fundamentals about the properties and application of IL in enhanced oil recovery (EOR); and their potential environmental effect. Finally, it may be concluded the main factor influencing the high toxicity of ILs is the hydrophobicity of the side chain. Therefore, further studies should be developed to design the sustainable LI for use in the EOR process.