The solubility of lithium oxide was measured in molten LiCl-KCl containing (58.5, 75, 90, and 100) mol % LiCl in the temperature range of (673 to 923) K. The melt with a higher content of LiCl has a higher solubility of Li(2)O. The pure LiCl has the highest solubility of Li(2)O, (12.0 +/- 0.2) mol % at 923 K. The estimated standard formal potential of O(2)/O(2-) increases linearly as the temperature decreases and as the mole fraction of LiCl increases.