The conductance of sodium diethyldithiocarbamate (NaDDC) has been measured in acetonitrile-water mixtures at 25°C where the dielectric constant (D) ranges from 46.52 up to 74.66. Using Fuoss-Onsager theory, the data was interpreted to obtain Λo, KA and å values. For NaDDC, the ion parameter å (express the solvation) and limiting equivalent conductance Λo decrease with decreasing the dielectric constant of the medium until it reaches a minimum and then increases again. The increase in log KA versus 1/D plot shows the dominance of electrostatic interaction. By applying the solvent separated – ion pair model, the association constant (KA) is analyzed.