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MnS inclusions in stainless steel can easily induce pitting corrosion, which seriously deteriorates the corrosion resistance of steel. Applying MnS inclusion control technology or modification technology is an effective way to improve the corrosion resistance of stainless steel. In this paper, the S32550 duplex stainless steel was taken as the research object, and the test steels with different Ce and Ti contents were smelted in a vacuum induction furnace under laboratory conditions. The modification effects of trace amounts of Ce and Ti on MnS inclusions in stainless steel and their effects on the corrosion resistance of stainless steel were studied by JSM - 6510 scanning electron microscope, periodic corrosion weight loss test, AC impedance test, Tafel polarization curve test and other test methods. Results showed that after adding 0.047% (mass fraction) Ce into the steel, the inclusions in S32550 steel changed from MnS into Mn - S - Ce - O composite ones, the size of the inclusions was decreased from about 14 μm to about 3 μm, and the corrosion rate was reduced by 63% compared with that before adding Ce. After adding 0.051% (mass fraction) Ti into the steel, the inclusions changed from MnS into Mn - S - Ti - N composite ones, and the size was decreased from about 14 μm to about 4 μm. The corrosion rate was reduced by 33% compared with that before adding Ti. Furthermore, after adding 0.052% (mass fraction) Ce and 0.054% (mass fraction) Ti, the inclusions changed from MnS into Mn - Ce - Ti - O composite ones, and the size was decreased from about 14 μm to about 2 μm. The corrosion rate was reduced by 76% compared with that before adding Ce and Ti. Therefore, adding Ce and Ti could both increase the capacitive arc radius and self - corrosion potential of the test steel and decrease their self - corrosion current, significantly improving the corrosion resistance of S32550 steel. Besides, the effect of Ce was better than that of Ti, and the effect of adding Ce and Ti together was better than adding Ce or Ti alone.