Electrical properties of glasses in the AgI-Ag2O-V2O5-P2O5 system, which in general case exhibit mixed electronicionic conduction, were investigated. By thorough adjustment of the composition we have prepared glasses with comparable electronic and ionic contributions to the electrical conductivity. The measured impedance spectra of these glasses indicate the important role of diffusion processes in charge transport. The spectra were analyzed numerically using an electrical equivalent circuit consisting of parallel electronic and ionic branches. The substantial role in the equivalent circuit is played by Warburg elements representing finite-length and semi-infinite diffusion phenomena occurring close to the electrodes.