Magnetic ionic liquids (MIL) are extensively used in extraction and catalytic processes. Here, a series of MIL, i.e., 1-n-butyric acid-3-methylimidazolium chloride/xFeCl(3) ([C(3)H(6)COOHmim]Cl/xFeCl(3); x=0.5, 1, 1.5, 2), were synthesized and characterized by infrared spectroscopy, visible absorption spectrometry, and electrospray ionization mass spectrometry. The MIL [C(3)H(6)COOHmim]Cl/2FeCl(3) was found to be highly active for the extraction and catalytic oxidative desulfurization of a model oil under mild conditions. Of note, the removal of benzothiophene, which has been regarded as a refractory aromatic sulfur compound, could be achieved at up to 100% in 10min. After reaction, the MIL could be easily separated from the model oil by applying an external magnetic field, due to its paramagnetic properties.