Abstract: Vaporization processes of the components in the La2C3–C system were studied by Knudsen effusion mass spectrometry in the temperature range of 2196–2435 K. The main vapor species over the system under study were La and LaC2. The temperature dependences of the partial pressures of the identified vapor species and of the La activity, as well as the La and LaC2 partial molar enthalpies of vaporization, were determined in the La2C3–C system. It was shown that the found values of thermodynamic properties are in agreement with the literature data and with the results of modeling using the NUCLEA database for the LaC2–C system. This allowed the thermodynamic properties of the LaC2–C system to be evaluated on the basis of the obtained values. It was established that the La activity is independent of temperature, indicating a zero La partial molar enthalpy of mixing in the region of the LaC2 and C equilibrium. The results of this study can be further used to supplement thermodynamic databases and to optimize phase diagrams of multicomponent carbide systems that are promising for various high-temperature technologies.