Phosphate promoted Na2WO4/Al2O3 catalyst with 10 wt.% tungsten was prepared by simple impregnation method. Analytical characterization results showed that tungstate and phosphate were uniformly dispersed in alumina matrix and its structural properties were preserved. The effect of phosphate as promoter in catalyst activity was studied using dibenzothiophine (DBT) as model oil and the results reveal that it plays an important role in oxidation activity of Na2WO4/Al2O3 catalyst, in addition, the catalytic activity of Na2WO4/Al2O3 was increased gradually with increasing phosphorus contents up to 2.5 wt.%. The catalyst was recycled and the results show that no significant decrease in catalyst activity was observed even after five recycled runs. We also applied our catalyst in oxidative desulfurization (ODS) of FCC diesel oil (with sulfur contents 4100 ppm), andmore than 92% of sulfur was removed from diesel oil under mild reaction conditions.