Abstract: The oxidative desulfurization of dibenzothiophene (DBT) in n-octane as model oil with Brnsted acidic ionic liquids (ILs) Nmethyl-pyrrolidonium phosphate (\Hnmp\H₂PO₄) as catalytic solvent and H₂O₂ as oxidant was optimized by orthogonal experiments. 99.8% of DBT in the model oil was removed under the optimal conditions of molar ratio of H₂O₂ to sulfur of 16∶1, reaction temperature of 60℃, reaction time of 5h, and volume ratio of model oil to ILs of 1∶1. The desulfurization efficiency of actual diesel was 64.3% under the optimized conditions. The influences of the desulfurization efficiency of DBT decreased in the following order: oxidation temperature > oxidation time> molar ratio of H₂O₂/sulfur (O/S) > volume ratio of \Hnmp\H₂PO₄ to model oil (VIL/Vmodel oil), according to extreme analysis of orthogonal test. The IL \Hnmp\H₂PO₄ can be recycled six times without a significant decrease in activity.