A catalytically cracked gasoline feedstock is desulfurized under reaction conditions of a hydrogen feed rate measured at the reactor inlet of from 1 to 5 mols per mol of the feedstock oil and of from 5 to 50 mols per mol of the olefin components contained in the feedstock oil, a reaction temperature of from 200.degree. to 300.degree. C., a total pressure inside the reactor of from 10 to 20 kg/cm.sup.2 G, and a liquid hourly space velocity of from 2 to 8 l/hr, and using a catalyst which comprises a support mainly comprising alumina and having a surface area of 200 m.sup.2 /g or larger, wherein MoO.sub.3 in an amount of from 10 to 20 wt % and CoO in an amount of from 3 to 6 wt % in terms of inner content are fixed to the support, and the weight ratio of MoO.sub.3 to CoO is from 2.5 to 4.5.