The excess enthalpies of liquid alloys in the ternary system Bi-Sb-Se were determined at 873 K in a heat flow calorimeter for five sections BiySb1 - Se-y with y = 0.2, 0.4, 0.5, 0.6 and 0.8 and for the section Bi0.5Sb0.5-Se at 773 K. The enthalpy surface in the ternary system is determined by a valley of exothermic minima stretching from 2 : 3 compositions Bi2Se3 to Sb2Se3 in the Liquid binaries. The excess enthalpies in the binary systems were adapted with the association model using the Lukas program. Ternary interactions were taken into account for the analytical description of the ternary system.