The electrical conductivity of liquid Cs-CsI has been measured from pure Cs to pure CsI. In the metallic range and down to conductivities of about 500 (ohm.cm) −1 thin walled metallic containers were used as sample cells. The measurements of the low conductivities were performed in Al 2O 3-ceramic cells with Nb electrodes using an ac-bridge for frequencies up to 10 KHz. The concentration dependence of the electrical conductivity of Cs-CsI is similar to that in Cs-CsCl but differs considerably from that in Cs-CsAu close to stoichiometry.