Thermal stability of calcium copper titanate was studied by differential scanning calorimetry, thermogravimetry and high-temperature mass spectrometry. Calcium copper titanate (CCTO) had no thermal effects and mass losses caused by thermal dissociation or any phase transitions, besides melting, in the temperature range of 298–1423 K. The melting point of calcium copper titanate is 1398 K. The endothermic effect at 1250 K was associated with the decomposition of copper (II) oxide segregated in the intergrain space of the CaCu₃Ti₄O₁₂-CuO ceramics. In this connection, we proposed a simple method for estimating the content of copper oxide in the CaCu₃Ti₄O₁₂-CuO composite. The processes of evaporation of CaCu₃Ti₄O₁₂ in the temperature range of 1500–2100 K were studied by high-temperature mass spectrometry. In the temperature range of 1500–1750 K, easily volatilized copper oxide was evaporated selectively from the calcium copper titanate. At the temperature of 2100 K, atomic calcium and titanium oxides, TiO and TiO₂, were present in the vapor.