Abstract: The oxidative desulfurization (ODS) of diesel oil in the presence of copper ion and hydrogen peroxide was investigated with ultrasonic irradiation as an extra energy. The effects of operation parameters such as the aqueous phase pH and ultrasonic power on the desulfurization efficiency were examined and the ODS mechanism under ultrasonic irradiation was suggested. The results showed that the sulfur removal rate increases at first, and then decreases with an increase in the aqueous phase pH; the highest sulfur removal rate is obtained at about pH = 2.00. ODS is in conformity with apparentfirst order kinetics for any of the four cases: with hydrogen peroxideacetic acid (without ultrasound), Fentontype reagent (without ultrasound), combination of ultrasound and hydrogen peroxide, and combination of ultrasound and Fentontype reagent. Moreover, the sulfur removal rate increases with the ultrasonic power, because the production of cavitation bubbles in the liquid and the collapse of the bubbles are enhanced by the ultrasonic power.