Polymer-supported sulfonium salt (PS) was synthesized by the reaction of sulfur-containing compounds, present in light oil, with iodomethylpolystyrene (IMP) and AgBF4. Dibenzothiophenes (DBTs) and benzothiophenes (BTs) in the oil were successfully anchored on the IMP as the corresponding sulfonium salts, via nucleophilic displacement of the iodide atom on IMP with the sulfur atom on DBTs and BTs. By this means, the sulfur content of the light oil was decreased successfully to the required deep desulfurization level (0.05 wt%). The PS, obtained from light oil, showed significantly high activity as phase transfer catalyst for the anion exchange reaction of 1-bromooctane with potassium thiocyanate in the organic/water two-phase system. This high activity for the PS results since the highly lipophilic alkyl-substituted DBTs and BTs are anchored on the PS as the sulfonium salts.