Abstract Calcium sulfides doped with tri- and tetravalent metal sulfides were prepared. Their electromotive forces (EMF) were measured on a galvanic cell(Fe+FeS| Solid Electrolyte| Cu+Cu2S) where the solid electrolyte was a material in a CaS–Ln2S3–MS2 system. The cell, using calcium sulfide doped with La2S3 and ZrS2, exhibited an EMF value as high as the one calculated for thermodynamical equilibrium. The CaS–La2S3–ZrS2 solid electrolyte showed, predominantly, an ionic conduction in the sulfur pressure range from 10−4 to 102 Pa with an activation energy of approximately 56.7 kJ·mol−1, which was lower than for CaS and CaS–La2S3.