Abstract <p>The ternary NaClO₃–C₂H₅COCSSNa–H₂O system was investigated in detail from a physicochemical perspective. During the study, the system was subdivided into binary subsystems and analyzed along six internal sections. Polythermal solubility data were obtained over the temperature range from –23.2 to 38.0°C, and a comprehensive polythermal solubility diagram of the system was constructed. The resulting diagram provides a complete representation of the temperature-dependent solubility behavior of the system components. Based on the constructed phase diagram, the crystallization fields of ice, NaClO₃, and C₂H₅COCSSNa were identified, and the boundaries between them were established. The results indicate that the system belongs to a simple eutonic type. This behavior demonstrates that the components crystallize independently without undergoing mutual chemical interaction, thereby preserving their individual identities. Furthermore, both salts exhibit high solubility in water, and the formation of stable solutions over a wide concentration range was observed within the system. Along the [40% NaClO₃ + 60% H₂O]–[C₂H₅COCSSNa] section, the physicochemical properties of solutions prepared at various ratios were comprehensively analyzed. In particular, the crystallization temperature, viscosity, density, pH of the medium, and refractive index were determined as functions of composition. The results demonstrated that variations in component concentration significantly influence the structural state of the solutions. Based on the experimental data obtained, a “composition–property” diagram was constructed. This diagram clearly illustrates the relationship between solution composition and its physicochemical properties and plays an important role in evaluating the practical application potential of the system. The findings may serve as both a theoretical and practical basis for the application of aqueous systems based on NaClO₃ and C₂H₅COCSSNa in technological processes.</p>