Abstract: To enhance the long-term corrosion resistance of the plasma electrolytic oxidation (PEO) coating on the magnesium (Mg) alloy, an inorganic salt combined with corrosion inhibitors was used for posttreatment of the coating. In this study, the corrosion performance of PEO-coated AM50 Mg was significantly improved by loading sodium lauryl sulfonate (SDS) and sodium dodecyl benzene sulfonate into Ba(NO₃)₂ post-sealing solutions. Scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectrometer, and ultraviolet–visible analyses showed that the inhibitors enhanced the incorporation of BaO₂ into PEO coatings. Electrochemical impedance showed that post-sealing in Ba(NO₃)₂/SDS treatment enhanced corrosion resistance by three orders of magnitude. The total impedance value remained at 926 Ω·cm² after immersing in a 0.5wt% NaCl solution for 768 h. A salt spray test for 40 days did not show any obvious region of corrosion, proving excellent post-sealing by Ba(NO₃)₂/SDS treatment. The corrosion resistance of the coating was enhanced through the synergistic effect of BaO₂ pore sealing and SDS adsorption.