Abstract: The effect of SO₄^2- on the passive and pitting behavior of 316L austenite stainless steel was investigated in a Cl^--containing solution using potentiodynamic polarization tests, electrochemical impedance spectroscopy tests, potentiostatic polarization tests, and galvanostatic polarization tests. In addition, scanning electron microscopy was used to observe the pitting morphology. The results show that the increased SO₄^2- concentration increases the passive region of 316L, makes the pitting potential more positive, and decreases the current density, indicating an improved pitting resistance. However, the pitting morphology shows a more complicated trend, and the roughness of the pits increases with the increased SO₄^2- concentration after pitting occurred.