<p><b>Abstract</b>—Previously published data on the density and electrical conductivity of molten salt mixtures containing alkaline metal and beryllium chlorides and fluorides are used for the calculation of the molar and equivalent electrical conductivities of the systems. The procedure of simultaneous measuring the temperature dependences of the density and conductivity of melts provides the most correct data for the calculation of molar and equivalent conductivities. As a rule, the shape of the isotherm of these properties reflects the interaction of the melt components. Conclusions about possible structural changes during the formation of a molten salt mixture are based on an analysis of deviations of the experimental molar and (or) equivalent conductivities from those calculated by model equations for systems with an ideal behavior of the components. The following two types of equations are most popular: linear equations according to which the conductivity of a mixture is summated of proportional contributions of the conductivity of the mixture salts and nonlinear second-order equations with respect to the component concentrations. The first type equations assume independent electricity transfer by each component of the melt, and the equations of the second type are based on the “pair exchange” mechanism; i.e., the conductivity act is related to contact of two like or unlike particles (charge carriers). The equations of both types are illustrated by the simplest model of hard spheres (charge carriers). Excess properties of the equivalent conductivity should be analyzed for the systems with different-charge components. The isotherms of the molar conductivity of the systems of alkaline metal and beryllium chlorides and fluorides and the dependence of the equivalent conductivity isotherms on the anionic composition of mixtures containing potassium and beryllium halides are presented. The relative excess deviations of the properties of these systems from the proposed nonlinear model of ideal electrical conductivity of the system taking into account molar volumes of the components are considered. Assumptions are advanced on a possible relationship of extremes of the relative excess properties to the interaction of components of the molten salt mixtures. As a whole, the influence of the anionic composition on the conductivity of the beryllium-containing molten salt electrolytes is similar to that observed earlier for molar volumes and fusibility of these salt mixtures.</p>