A desulfurization process for light oil has been investigated using a polymer-supported imidation agent (PI, sodium N-chloro-polystyrenesulfonamide). When n-tetradecane solution (model light oil) containing dibenzothiophene (DBT) was stirred with methanol in the presence of PI and acetic acid at a temperature of 323 K, DBT was chemically adsorbed on the PI, via the imidation of sulfur atoms on DBT by the PI, and removed successfully from the oil. The polymer obtained was insoluble to the solutions and could be recovered by filtration. The present process was found to be also effective for the desulfurization of actual light oil: the sulfur concentration of commercial light oil was decreased successfully from 400 ppm to less than 50 ppm (ultra-deep desulfurization level).