Abstract: The corrosion behavior of micro-arc oxidation (MAO) coating on AZ91D magnesium alloy in ethylene glycol aqueous solution was investigated using electrochemical impedance spectroscopy (EIS) and relative equivalent circuits. Scanning electron microscopy (SEM) was employed to examine the surface morphologies of samples after corrosion. The results show that the ethylene glycol adsorbed and formed a layer of protective film on the surface of MAO coating; with increasing concentration of ethylene glycol the charge transfer resistance increased, and the corrosion resistance of MAO coating on AZ91D magnesium alloy improved. Corrosive ions (Cl- and SO42-) coexisting in ethylene glycol aqueous solution enhanced corrosivity of the MAO coating. The corrosion of AZ91D magnesium alloy coated MAO was effectively inhibited by addition of 0.2 mol·L-1 NaF because the insoluble fluoride containing crystals filled the interspaces in porous layer of the MAO coating.