In order to improve the corrosion resistance property and the bone biological activity of medical magnesium alloys, the ceramic coatings were prepared on AZ91D alloy by micro-arc oxidation in the solution of zirconium salt system and the silicate system solutions, respectively. The phase compositions of the ceramic coatings were analysed by XRD instrument. The surface morphologies and the distribution of calcium, phosphorus were also researched by SEM and EDS. The results show that the ceramic coating in solution of zirconium salt system mainly consists of ZrO2 and MgF2, and the ceramic coating in solution of silicate system mainly consists of MgSiO3 and MgO. No corrosion of ceramic coatings is obsevred during the Hank’s simulated tests, which indicates that the ceramic coatings can improve the corrosion resistance properties of AZ91D. The SEM observation results show that agglomerates on the surfaces of the ceramic coatings are found during the testing from 7 to 14 d, and a worm-like hydroxyapatite morphology appears on the surface after testing for 21 d. The contents of calcium and phosphorus elements on the ceramic coating surface increase gradually with the increasing of testing time, and the Ca/P ratio on the ceramic coating in solution of the zirconium salt system is 1.445, which is close to the hydroxyapatite Ca/P ratio (1.67)