Micro-arc oxidation (MAO) layers which were prepared on magnesium alloy WE42 and AM20 by MAO were sealed with PLLA by immersion technique to get composite coatings. The microstructure of the MAO coatings and the composite coatings were analyzed by scanning electron microscopy. The composition of MAO coating is MgSiO3 and SiO2 by X-ray diffractometer (XRD) and the rate of mass loss were tested by immersion test. Electrochemical impedance spectroscopy (EIS) shows that PLLA coating seals the pores in the MAO coating and improves the corrosion resistance by preventing the corrosive ions from diffusing to the magnesium alloy substrate. This composite coating is of high biocompatibility so it is of significance to improve the property of bioabsorbable magnesium stent.