Magnesium and its alloys have shown great potential as promising biodegradable implantation materials. However, rapid biodegradation has limited them to clinical applications. To overcome this disadvantage, a Ca/P coating was formed on AZ31B magnesium alloy by micro-arc oxidation (MAO) in three different electrolytes with and without hydroxyapatite (HA). The surface properties were determined by scanning electron microscope (SEM), X-ray diffraction (XRD), and micro-hardness tester. Immersion tests, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) tests were employed to evaluate the corrosion behavior of MAO coatings on AZ31B magnesium alloy in simulated body fluid (SBF). The results revealed that the pore size and the micro-hardness would be changed by the different electrolytes. The electrochemical corrosion tests show that the sample prepared in the electrolyte containing 4 g/L edetate calcium disodium (C 10 H 12 N 2 O 8 CaNa 2 Á 2H 2 O, EDTA-Ca), 1.5 g/L sodium hexametaphosphate (NaPO 3 ) 6 , 2 g/L sodium hydroxide (NaOH), and 15 g/L sodium metaaluminate (NaAlO 2 ) with 1.5 g/L HA has the smallest corrosion current density and the largest electrochemical impedance.