The electrical conductivities of sodium polysulfide melts, Na2S4 and Na2S5, were measured as a function of temperature between 300 and 360 degrees C. Due to the viscous nature of the sodium polysulfide melts, the conductance cells are axisymmetric cylindrical cells with a microelectrode, instead of capillary cells. The values of the Arrhenius activation energy derived from the experimental conductivity data are about 33 kJ/mol. The macroscopic model of sodium polysulfide melts has described the melts as composed of sodium cations, monosulfide anions, and neutral sulfur solvent.(1) For this model, the binary interaction coefficients quantifying the interaction between sodium cations and monosulfide anions were calculated from the experimental conductivity data and literature data for the transference number, diffusion coefficient, activity coefficient, and density.