Lead, in comparison with other metals, has low chemical activity and high corrosion resistance. Complex alloying of lead with antimony, tellurium and copper in optimal concentrations made it possible to obtain highly effective alloys for protective cable sheaths. Pb – Sb – Cu – Te lead alloy provides the cable sheath with high resistance to fatigue, creep and active deformation in a wide temperature range, as well as good manufacturability. The basis for such a complex of positive characteristics is a specific fine-grained thermostable structure, which determines the stability of properties in operation. Alloys of this composition are at the level of world standards: they have the best complex of operational and technological characteristics compared to the most promising domestic and foreign analogues. In the work, the heat capacity of the alloys of the Rb – Te system was determined in the "cooling" mode by the known heat capacity of a reference sample made of copper grade M00. Polynomials describing the temperature dependence of the heat capacity and changes in the thermodynamic functions of alloys are obtained. It isfound that with increasing temperature and tellurium content, the heat capacity, enthalpy and entropy of lead increase slightly, and the Gibbs energy values decrease.