Elimination of nitrogen (N) compounds contained in fuel oils is one of the essential processes for petroleum refinery due of their hindering consequences on the hydrodesulfurization (HDS) process. Traditional hydrodenitrogenation (HDN) techniques have some barriers to produce lower-N or N-free fuel oils, e.g., HDN is less effective to remove some cyclic N-compounds; HDN is expensive because of operating conditions such as high pressure and high temperature, and also requires the presence of an expensive catalyst and hydrogen. Application of ionic liquids (ILs) for the purpose of fuel oil extractive denitrogenation (EDN) has been an important part of research in recent years, and it has shown huge potential as an effective substitute or supplemental technique to HDN. In the present review, we studied research results of EDN using ILs and have discussed widely the diversified factors influencing denitrogenation. This review concludes that EDN employing ILs has a promising future owing to the ideal physical and chemical characteristics of ILs; though for such a new technology there are some challenges, for which a discussion is also given. This review contributes proposals for possible commercial application of ILs in EDN.