Novel Bronsted-Lewis acidic ionic liquids having a protonated N-octylcaprolactam-based cation and Cl/nZnCl(2) anion (n = 1, 2 and 3) were synthesized and investigated as catalysts in the oxidative desulfurization (ODS).of both model oil and real diesel fuel, with hydrogen peroxide (H2O2, 30 wt%) as oxidant. It is observed that the ODS performance increases significantly with the increase of ZnCl2 proportion. Then detailed experiments for the ODS of model oil were carried out with [Hnoc]Cl/3ZnCl(2) to investigate the influence of some important factors, including reaction temperature, molar ratio of H2O2/S, ILs dosage, initial S-content and sulfide species. It is worth noting that, with the mass ratio of ILs/oil of only 1:20, satisfactory conversion rate can also be achieved for the removal of dibenzothiophene (DBT), and the ILs were used for six cycles without a noticeable decrease in activity. What is more important, the ILs can reduce the S-content of a real diesel from 559.7 ppm to 8.2 ppm with 98.5% sulfur removal rate and 96.3% diesel recovery through a one-step ODS process. Deduced from the GC-PFPD spectra, almost all the original S-compounds and their oxidized products were completely converted and extracted, respectively. The outstanding desulfurization efficiency can be attributed to the good phase transfer property of the ILs. (C) 2016 Published by Elsevier B.V.