The e values in the internal cation mobilities of (Li,K,Cs)N0 3 of the eutectic composition (35.2-39.8-25.0 mol%) in the temperature range from 453 to 673 K were measured by Klemm's countercurrent electromigration method, where e is defined as (bj-6j)/6 a ; b. d is the average internal cation mobility and the subscripts i and j refer to any two out of these three cations. The conductivity was measured by a direct current method. From these data and the molar volume calculated from those of the pure salts on the assumption of additivity, the internal cation mobilities, b Ll , b K and b Cs , have been calculated. The b u is well expressed by the empirical equation presented for binary alkali nitrates; the negative devia-tion for b K and b Cs may be accounted for on the assumption of the tranquilization effect of Li + . The or-ders of those internal cation mobilities are b Cs <b K <b Li at 453^73 K, b Cs <b Li <b K at 473 -583 K, and b u <b Cs <b K at 583-673 K. These orders can be interpreted in terms of the dynamic dissociation mod-el previously presented.