Superionic conducting glasses in the Agl-Ag2O-V2O5 system were prepared by heating the appropriate amounts of raw materials at 723 K and quenching in liquid nitrogen. The polycrystalline materials were prepared by slowly cooling the melt to room temperature. X-ray diffraction was used for material characterization. The electrical conductivity of the pulverized samples, pressed together with an electrode mixture of silver and electrolyte (1:2 by weight) under 5000 kg cm-2 pressure to form pellets 10 mm in diameter and 2 to 3 mm in thickness, was measured in the temperature range 300 to 365 K at 1 kHz. The ionic conductivities of the glasses were always higher than those of their polycrystalline counterparts, while their activation energies were also slightly higher. Conductivity measurements on annealed glassy samples indicated that the conductivity decreases with the time of annealing, and reaches a constant value which is nearly the same as that of the polycrystalline sample. Electronic conductivities of both types of sample were obtained by using Wagner's polarization cell technique, which showed that the electronic conductivity for both types was five orders of magnitude less than the total conductivity. Typical galvanic cells having the configuration Ag,electrolyte/electrolyte/C,electrolyte,I2 were constructed and the silver ion transport number was calculated by the e.m.f. method. © 1987 Chapman and Hall Ltd.