Annotation. Problem. The problem is to obtain a database on the structure and properties of Pb-Sn solders, which are widely used in radio engineering. Target. The purpose of this work was to study the influence of the chemical composition of low-melting solders of the Pb-Sn system on the main mechanical properties and structure. Method. To achieve this goal, a complex of metallographic, mechanical and analytical studies of samples in the initial state was carried out. Results. The hardness of POS-40 and POS-61 solders turned out to be significantly higher compared to the hardness of the pure components from which they are formed. Mechanical studies have shown that the strength characteristics in POS-40 solder are lower, and ductility is higher than in POS-61. Both alloys had approximately the same relaxation properties and within 100 seconds the stress decreased by 70-80%. These data testify to the high ability of the materials that were studied to relieve stresses arising in the junction. Metallographic studies have shown that the structural state of the alloys that have been studied corresponds to the Pb-Sn diagram. The data obtained as a result of research on the properties and structure of POS-40 and POS-61 solders can be used in practice.