An organic electroluminescent device including a lower electrode, an organic light-emission medium, and an upper electrode on a support substrate, wherein the water content of the organic light-emission medium does not exceed 0.05 wt. %. By so controlling the water content of the organic light-emission medium, it is possible to prevent shrinkage of a light-emission area based on production of non-emission parts or non-emission spots for a long time at both high temperature and room temperature conditions. A method of making the organic electroluminescent device is disclosed also.