Magnesium is involved in many essentials physiological functions in cells and protects yeast against ethanol stress. There are any articles about the influence of magnesium on the process of wine fermentation of musts with high sugar concentration. In our previous work we observed the favorable influence of 240 mg/dm3 magnesium on the fermentation of the musts with sugar concentration about 320 g/dm3. The results in present study show that the addition of 760 mg/dm3 magnesium to the musts causes higher amount of ethanol in wine, higher fermentation efficiency and yeast viability.