Bronsted acid ionic liquid, N-methyl-pyrrolidonium tetrafluoroborate ([Hnmp]BF4), was employed as an extractant and a catalyst to remove dibenzothiophene (DBT) from model oil in the presence of H2O2. The kinetics and mechanism of DBT oxidation by [Hnmp]BF4 and H2O2 were proposed. DBT Could be effectively removed from the oil phase by this process. Most of the oxidative products were in the ionic liquid phase for their higher polar property without additional extraction by solvent. The room-temperature ionic liquid [Hnmp]BF4 could be recycled 7 times without it significant decrease in the desulfurization activity.