The phosphotungstic acid/mesoporous graphitic carbon nitride catalyst was successfully prepared by immobilizing phosphotungstic acid (H3PW12O40, HPW) on mesoporous graphitic carbon nitride (mpg-C3N4). The prepared series of HPW/mpg-C3N4 catalysts was characterized via X-ray diffraction, nitrogen adsorptiondesorption isotherm, Fourier transform infrared spectroscopy, transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy, and thermogravimetric analysis. Results showed that the Keggin structure of HPW active species is still kept after being immobilized on the mpg-C3N4 surface. The HPW/mpg-C3N4 catalyst showed a high catalytic activity in the oxidative desulfurization process. Dibenzothiophene can be removed completely under optimal reaction conditions, and no significant decrease in the catalytic activity of the catalyst was observed after 15 recycles.