The oxidative desulfurization (ODS) of real diesel fuels, including a commercial diesel with 340 ppmw of sulfur and a low-sulfur diesel with 45 ppmw of sulfur by using molecular oxygen as an oxidant has been carried out and studied. At 140 oC under oxygen bubbling for 2 hours in the absence of catalyst, most sulfur compounds in both diesel fuels have been oxidized to corresponding sulfones. These sulfones are easy to be removed by adsorption on activated carbons. The results show that molecular oxygen directly participates the oxidation of dibenzothiophenes in real diesel fuels and is indispensable to achieve the oxidative desulfurization process. This study indicates that the developing ODS process with molecular oxygen as an oxidant is promising for ultra-deep desulfurization of diesel fuels.