During the two years field experiment the effect of three treatmens (NPK,NPK+15 kg Mgha-1, NPK+30 kg Mg ha-1) on photosynthesis .chlorophyll contamination and corn yield was observed. Magnesium nutrition had an effect oh chlorophyll increase in leaves just by corn-cob. Photosynthesis intensity has been increasing under effect of magnesium addition in the both studied plant growing stages. Magnesium has been also affected on the total corn dry mass yield increase and on the corn-cob yield. In the specific experiment conditions the best rate was the rate of 15 kg Mgha-1.