Fluorozirconate glasses have been prepared and their ionic conductivity measured as a function of composition and temperature. All compositions are good fluoride ion conductors with conductivities at 250°C in the 10-6-10-5 (Ω-cm)-1 range and activation energies between 0.7 and 0.9 eV. The fluoride ion to metal ratio was varied in the ZrF4/1bBaF2/1bThF4/1bNaF system by replacing ZrF4and/or BaF2 with NaF. When Na+ substitutes for Ba+2 a systematic decrease in the conductivity, σ, and the activation energy, Ea, is seen. This is explained on the basis of a reduction of carriers and on the modification of the network by Na+ ions. No systematic variation in σ or Ea were seen when Na+ replaces Zr+4. A change in slope of the log σ vs 1/T plot was seen at the glass transition temperature in La-containing glasses. © 1980.