The investigations of the physical properties of solid solution (AgxCu1-x)Br have been reviewed. Structural analysis by X-ray diffraction was given first. The diffraction data were interpreted as an evidence for a massive disorder with cation interstitial concentrations increasing with amounts of Cu+ ions in AgBr. Next the disordered distribution of cations was examined from a thermodynamical point of view. The electrical conductivities and transport numbers of the solid solution (AgxCu1-x) Br have been measured as a function of temperature and composition in order to investigate the contribution of Cu+ dissolved in AgBr to the transport properties. The enthalpies of formation and migration for cations show an exponential decrease with increasing amount of Cu+ into AgBr lattice. The lowering is attributable to the lattice expansion by the occupation of Cu+ at the interstitial sites. The effect of exponential decrease in the formation enthalpy is to allow a rapid growth in the concentration of interstitials around the composition of x=0.85. The creation of massive defects is probably responsible for the high ionic conductivity in the solid solution of this system.