A novel heterogeneous catalyst was prepared by supporting the ionic liquid (IL) 1-octyl-3-methylimidazolium hydrogen sulfate ([Omim][HSO4]) in the silica-gel matrix using a sol-gel method and employed in oxidative desulfurization of a model oil containing dibenzothiophene (DBT) and real diesel fuel. The properties of the supported ionic liquid (SIL) were characterized by FT-IR, TGA, BET-BJH, SEM-EDS, and PSA. The results showed that the ionic liquid was successfully incorporated in the silica-gel matrix, and a catalyst having high surface area was prepared. The effects of H2O2/DBT molar ratio (O/S), temperature, SIL/oil mass ratio, initial S content, and sulfur species on the sulfur removal of the model oil were studied. The highest DBT removal efficiency of 99.1% was obtained with the prepared catalyst having 17 wt % supported IL loading in the conditions of SIL/oil (w/w) of 1:3 and O/S molar ratio of 5 in 50 min at 50 degrees C. The prepared catalyst can be efficiently applied in oxidative desulfurization with consumption of much lower IL compared to that in a desulfurization system using bulk IL. The order of oxidative removal efficiencies of different sulfur species is as follows: DBT > BT > TS > 4,6-DMDBT. The SIL can be separated by a simple filtration from the reaction system and reused four times without any significant decrease in its performance. A high sulfur removal of 75.7% was also obtained by applying the prepared catalyst in desulfurization of the hydrotreated real diesel fuel.