Synthesis and study of the physicochemical properties of silsesquioxanes modified with 3-aminopropyl, 2-aminoethyl-3-aminopropyl, and dithiooxamide groups was carried out. The obtained sorbents were characterized by thermal stability, porosity, and a high degree of functionalization; the concentration of groups grafted to the particle surface reached 2.80 mmol g-1. Modified silsesquioxanes were used as an electroactive substance for the development of indicator carbon paste electrodes (CPEs). When using a CPE with a 5% dithiooxamidated silsesquioxane content, the conditions selected for potentiometric titration of aqueous solutions containing silveri were pH 3-4, the titrant was potassium iodide. The designed sensor was successfully tested by analyzing a standard sample and a drug for silver ion content.