Three peroxo-molybdenum amino acid complexes (PMAACs) were synthesized and characterized. Their catalytic activities for oxidation of dibenzothiophene (DBT) in extraction and catalytic oxidative desulfurization system (ECODS) were evaluated using different ionic liquids. Comparing with simple catalyst Na(2)MoO(4)center dot 2H(2)O in ECODS, PMAACs were effective wide-ranging catalysts and exhibited high desulfurization efficiency not only in water-miscible IL [bmim]BF(4) but also in water-immiscible [bmim]PF(6), [omim]BF(4) and [omim]PF(6). Especially 4,6-dimethyldibenzothiophene (4,6-DMDBT), the most difficult refractory compound in HDS, could be completely removed under optimal conditions. The reaction mechanism and desulfurization differences between using Na(2)MoO(4)center dot 2H(2)O catalyst and PMAACs in water-miscible and water-immiscible ionic liquids have been investigated and explained by UV-vis. Kinetic parameters of the oxidation of DBT, BT and 4,6-DMDBT were studied. (C) 2010 Elsevier B.V. All rights reserved.