The solubility of Co oxide in (Li0.62K0.38)(2)CO3 melt has been studied in CO2-O-2 atmospheres at 873 similar to 1073 K. The stable phase of Co oxide in the melt was LiCoO2 under O-2 and CO2. At high CO2 pressure (P-CO2 > 0.1 atm) the acid dissolution was observed and the solubility of Co oxide was proportional to P-CO2(1.5). Although the solubility was lower than that for NiO, the pressure dependence was larger. The acidic dissolution reaction is estimated to be LiCoO2 + 3/2CO(2) --> Li+ + Co2+ + 3/2CO(3)(2-) + 1/4 O-2 At low CO2, pressure (PCO2, < 0.01 atm) basic dissolution was observed and the reaction is estimated to be LiCoO2 + 1/2CO(3)(2-) + 1/4 O-2 --> Li+ + CoO32- + 1/2CO(2)