Ag-x(Ge0.25Se0.75)(100-x) (10less than or equal toxless than or equal to25 at.%) ionic conductor glasses, prepared by a melt-quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz-2 MHz at different temperatures T from room temperature to 363 K. The conductivity of the glasses sigma was obtained as a function of the silver concentration and the temperature. The temperature dependence of the ionic conductivity follows an Arrhenius type equation sigma=(sigma(0)/T) . exp(-E-sigma/kT). The activation energy of the ionic conductivity E-sigma and the preexponential term sigma(0) were calculated. It was found that the room temperature conductivity increases by a factor of about 10 with increasing silver content (1.32 10(-5) S cm(-1) at x=10 and 1.09 10(-4) S cm(-1) at x=25), while the activation energy decreases from 0.367 to 0.339 eV The diffusion coefficient of the Ag+ ions was estimated. In addition, a model proposed by Elliott was applied to determine the activation energy of conductivity in the high-modifier-content region. The results are discussed in connection with structural aspects and with those published in the literature related to other chalcogenide and chalcohalide systems. (C) 2004 Elsevier B.V. All rights reserved.