The excess enthalpies of liquid binary Sb-Te alloys and of the ternary Pb-Sb-Te system were determined in a heat-flow calorimeter along the sections PbySb1-yTe with y=0.2, 0.5 and 0.8 at 1173 K and with y=0.5 at 1073 K. The largest values of the exothermic enthalpies are found on a line stretching from PbTe to Sb2Te3. The association model with additional ternary interaction parameters was applied for the analytical description of the ternary melt. In addition, the phase equilibria were determined by DTA and X-ray diffraction measurements. The thermodynamic functions of the quasi-binary sections PbTe-Sb and PbTe-Sb2Te3 were optimized and the phase equilibria calculated.