Electrical conductivity is one of the most important physico-chemical parameters in chemical engineering as well as in the technology of many industrial process. Especially in the metals production by the electrolysis from molten salts or metals recovery from slags in the electric furnaces, where the great energy is needed.In this work the continuously varying cell constant (CVCC) technique for measuring conductivity of non-ferrous slags and molten salts was used. This is high-accuracy technique, which requires no calibration. The technique was verified by measuring conductivity of standard KCl solution and molten KCl. A good agreement was obtained between measured and commonly accepted literature values. The results of measured conductivity of KF-AlF3 melts were compared with data obtained by other authors. It was proved that CVCC technique can measure accurately the electrical conductivity of high-temperature molten salts and metallurgical slags.