Investigated were the structure, the phase composition and the distribution character of alloying elements in the structure of heat-resistant alloy 45Х26НЗЗС2Б2 in the cast state. Revealed were liquation of chemical elements in the y-solid solution and carbide eutectic in the alloy and the formation of inclusions consisting of both carbides of niobium and nitrides of titanium. Thermodynamic instability of the cast structure of the investigated alloy was justified.