In a base solution containing 10g/L sodium hydroxide and 12g/L phytic acid, the influence of sodium silicate concentration on the formation and properties of anodic coatings obtained by micro arc oxidation (MAO) on magnesium alloys was systematically studied. The results demonstrate that sodium silicate can increase the solution conductivity, decrease the final voltage and change the coating color. Amorphous magnesium silicate is detected and the silicon content in the coatings continually increases with the increasing of sodium silicate concentration. Silicate ions can simultaneously combine with magnesium and aluminum ions to develop anodic coatings, while phytic acid radicals preferentially react with magnesium ions. Sodium silicate can further improve the corrosion resistance of MAO treated magnesium and the coating shows the best corrosion resistance in the base solution with 10g/L sodium silicate. ► Sodium silicate can change the coating color. ► Silicate ions combine with magnesium and aluminum ions to develop anodic coatings. ► Sodium silicate competes with phytic acid for taking part in coating formation. ► Sodium silicate improves the corrosion resistance of MAO treated magnesium alloys.