Effects of co-existing nitrogen compounds and polycyclic aromatic hydrocarbons (PAH) on oxidative desulfurization (ODS) of middle distillates with cumene hydroperoxide over a MoO₃/Al₂O₃ catalyst were quantitatively studied by using three different feedstocks with different concentrations of nitrogen and aromatic compounds in a batch reactor system at atmospheric pressure and 75 °C. It was found that there are strong effects of the co-existing nitrogen compounds and PAH on the ODS rate constants of 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, and such effects can be expressed as a linear function of the nitrogen and PAH concentrations, or nitrogen concentration and density of the feedstock. Analysis of the nitrogen compounds in feedstock and product oil confirms that the nitrogen compounds were involved in the oxidation reaction, which indicates that the co-existing nitrogen compounds in the feedstock can also be removed simultaneously in the ODS process. The ODS mechanism with oil-soluble oxidants in the presence of nitrogen and aromatic compounds was discussed.