In this work, a PEO coating on AZ31 magnesium alloy was post-treated in three different solutions containing NaF, Na2CO3 and NaAlO2, with the aim of sealing the anodic film and consequently increasing the corrosion resistance of the material. The morphology and chemical composition of the resulting coatings were analyzed by scanning electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. Samples were tested in a salt spray chamber, and corrosion rate was evaluated by the hydrogen evolution technique. It was found that a pore sealing treatment of 90 minutes in the solution containing a mixture of NaF and NaAlO2 resulted in an increase in the corrosion resistance of the PEO coating. © 2022, ASM International.