The experimental method for the high-temperature reaction equilibria in the AlN-Al2O3 system has been established. The equilibrium N-2-CO gas compositions coexisting with AIN-AI(2)O(3)-graphite have been successfully measured by quadrupole mass spectrometry and gas chromatography. From the obtained results, the standard Gibbs energy change of the forming reaction of AIN by carbothermaI nitridation is determined at temperatures ranging from 1723 to 1899 K: Al2O3(S) + 3C(s) + N-2(g) reversible arrow 2AIN(s) + 3CO(g) Delta(r)Gdegrees (kJ) = 711.2 - 0.3534T( +/-1.0) From the obtained result, the standard Gibbs energy of formation of AIN and the third-law enthalpy of formation of AIN at 298.15 K are derived as Delta(f)Gdegrees(AIN)(kJ/mol) = -316.2+0.1157T(+/- 0.5) Delta(f)Hdegrees(298.15K) (AIN)(kJ/mol) = -308.2(+/- 0.5) The disagreement between the present results and values in the NIST-JANAF thermodynamic table is discussed.