The vaporization of the solid alloys of the Ti-Al-Nb system has been extensively studied, with emphasis on the ␣ 2 -Ti 3 Al, (␣ 2 -Ti 3 Al ϩ ␥-TiAl), and ␥-TiAl phase fields, by using Knudsen effusion mass spectrometry at temperatures between 1170 and 1635 K. Twenty-four alloy samples of different compositions, were investigated and their Ti and Al partial pressures were determined. The thermodynamic activities of Ti and Al, as well as partial enthalpies and entropies of mixing, were evaluated for the mean temperature of 1473 K. The data obtained are discussed with respect to their significance for high-temperature corrosion of titanium aluminides and the solubility behavior of Nb in the ␥-TiAl phase.