The interaction of oxygen and gallium-free ions in molten NaCl–2CsCl eutectic in the temperature range of 823–923 K in an inert gas atmosphere was studied by the method of the potentiometric titration. The experiments were carried out in a two-electrode electrochemical cell using a standard YZM electrode as an indicator, which was made from ZrO2 stabilized by Y2O3. It was used to monitoring the activity of oxygen ions in the melt under study. The measurements were performed versus the standard reference chlorine electrode. The change of the composition of the salt mixture was carried out by dropping the calculated amount of lithium oxide samples without modification of the composition of the gas atmosphere. Gallium was introduced into the melt by anodic dissolution. On the titration curve of the molten NaCl–2CsCl–GaCl3 solution at pO2– – x coordinates, the equivalent point corresponding to the formation of gallium oxychloride, GaOCl, is clearly fixed. The equivalent points at the x values of 0.5 and 1.5 are not fixed. The first indicates at the absence of monovalent gallium ions in the molten salt and the possible formation of Ga2O gallium oxide, and the second is associated with the kinetic difficulties of the solid-phase reaction of Ga2O3 formation. Analyzing the curves of the potentiometric titration, the mechanism of the formation of gallium oxychloride and gallium one-and-a-half oxide was established. Using the material balance equations and solubility constants, the solubility of GaOCl and Ga2O3 in the molten solution under study was calculated. The experimental dependences of the solubility constants of GaOCl and Ga2O3 compounds as a function of temperature in the molten NaCl–2CsCl eutectic are described by the following equations: pKGaOCls=−7.55+16310T±0.02,pK_{{\text{s}}}^{{{\text{G}}{{{\text{a}}}_{{\text{2}}}}{{{\text{O}}}_{{\text{3}}}}}} = - 17.66 + \frac{{40{\kern 1pt} 410}}{T} \pm 0.02.$ The principal thermodynamic characteristics of oxychloride and gallium one-and-a-half oxide in molten NaCl–2CsCl eutectic were calculated.