Thermodynamic properties of matildite (Β-AgBiS2) in equilibriumwith sulfur and bismuth have been studied by anEMF method, using the fast Ag+ ion-conducting solid electrolytes gI and RbAg 4I5. The ternary phases were synthesized from the pure binary compounds. Properties of the electrolytes used have been reviewed, and their usage as pure conductors ofAg+ ions in the temperature ranges of the electrochemical cells employed was well defined. The EMF measurements were carried out using the solid-state electrochemical cells Pt(-)|Ag|RbAg 4I5Β-AgBiS2+AgBi3S 5+S|Pt(+) and Pt(-)|Ag|AgI|Β-AgBiS2+AgBi 3S5+Bi|C|Pt(+), in the temperature range 325-464 K. Based on the obtained results, thermodynamic functions for the formation ofmatildite (Β-AgBiS2) at sulfur and bismuth saturation have been determined. The obtained experimental values have been compared with the available literature values. New experimentally determined thermodynamic properties of the bismuth-saturated matildite (Β- AgBi1+xS 2) and sulfur-saturated matildite (Β-AgBiS2+ y) were generated and analyzed in detail.