The specific conductivity of molten LiCl-PrCl 3 , RbCl-PrCl 3 , and CsCl-PrCl 3 was measured from the liquidus temperature up to ∼1180 K by a conventional ac technique. The molar conductivity Λ was calculated by using literature data on the densities of the binary systems. In all cases, it was found that the plot lnΛ vs. 1/T is not a straight line. Thereby the activation energy of the conductivity does not remain constant but reduces with increasing temperature. In the specific and molar conductivity isotherms, strong deviations from additivity are observed with maxima in a range 35 -45 mol. % PrCl 3 . The results conform to the idea of dominating octahedral local coordination of Pr 3+ ions over the entire concentration range.