The influence of sodium borate concentration on the formation and properties of anodic coatings obtained by micro arc oxidation (MAO) on magnesium alloys was systematically studied in an alkaline solution with addition of 0-40 g/L sodium borate. It is shown that sodium borate can decrease the solution conductivity, take part in the coating formation and increase the coating thickness. With the increase of sodium borate concentration, the boron content in the coatings increases in the range of 10-20 g/L but decreases within the range of 20-40 g/L. Sodium borate cannot further improve the corrosion resistance attributed to the development of porous or rough anodic coatings. (C) 2012 Elsevier B. V. All rights reserved.