The amorphous Mg-based alloys may be used as metallic biomaterials for resorbable orthopedic implants. The Mg-Zn-Ca metallic glasses demonstrate variable in time degradation rate in simulated body fluid. In this work the Mg₆₆Zn₃₀Ca₄ alloy was chosen as a substrate for coatings. This paper reports on the surface modification of a Mg₆₆Zn₃₀Ca₄ metallic glass by plasma electrolytic oxidation (PEO). The structure characterization of uncoated Mg₆₆Zn₃₀Ca₄ alloy was performed by using TEMand XRD method. The immersion tests of coated and uncoated Mg₆₆Zn₃₀Ca₄ alloy were carried out in Ringer’s solutionat 37°C. The volume of released hydrogen by immersion tests was determined. The coatings structure and chemical composition after immersion tests by SEM/EDS were studied. Based on SEM images of surface structure samples, immersion tests results and hydrogen evolution measurement was proposed the course of corrosion process in Ringer’s solution for Mg-based metallic glasses with PEO coating. Results of immersion tests in Ringer’s solution allowed to determine the amount of evolved hydrogen in a function of time for Mg₆₆Zn₃₀Ca₄ metallic glass and sample with PEO coating. In comparison to the non-coated Mg₆₆Zn₃₀Ca₄ alloy, the sample with PEO layer showed a significantly decreased hydrogen evolution volume.