Total electrical conductivities and transference numbers of the AgxCu1-xI in the alpha-phase were measured as a function of temperature and composition. In this phase, it has been recognized that both Ag and Cu ions could be mobile and, in addition, the activation energies for both mobile ions are nearly the same. A structure refinement for this phase shows that both Ag and Cu ions vibrate at the 12d site with a large anharmonicity. However, the lattice constant obeys Vegard’s law. This result indicates that both mobile ions have the same conducting path although their amplitudes of anharmonic thermal vibrations are different.