The electrical conductivities of molten LiF–YF 3 and LiF–NaF–ZrF 4 have been obtained from impedance measurements and molecular dynamics simulations, and discussed through the analysis of the local structure of the liquid. The conductivity decreases with addition of MF n (M n+ =Y 3+ or Zr 4+ ) in the melt due to the formation of MFxn−x units, which can be either isolated or linked via bridging fluorine. Structural differences have been put in evidence depending on the nature of the multivalent metallic species (Y 3+ and Zr 4+ ) added in the alkali fluoride solvent regarding the stability of the MFxn−x units and the length m of [MFxn−x]m chains. These differences are at the origin of a more pronounced decrease of the electrical conductivity in the Zr-containing fused salts in the low MF n concentration régime.