Phase equilibria in the Bi–Sb–Sn ternary system have been studied experimentally as well as by using the calculation of phase diagram (CALPHAD) method. New experimental SEM-EDX and DTA results were used together with the literature data in this thermodynamic assessment. Solubility of bismuth in SbSn phase and ternary corrections for Liquid and Rhombo_A7 phase were established. Calculated values of thermodynamic functions were collated with recently published experimental thermodynamic results for liquid phase at 900K. Calculated isothermal sections at 200°C and 300°C were compared with our own experimental results based on the SEM-EDX analysis of composition of phases. Three calculated vertical sections were successfully compared with the DTA results from this work and from literature data. Reasonable agreement between calculation and experimental data was observed in all cases.