The electrical conductivity of silver iodide pressure moulded into pellets at 2.0 tons/cm2 was measured and the crystal structure of was investigated by means of x‐ray diffraction. The conductivity of decreases gradually as the heating and cooling operations are repeated. The decrease is attributed to the phase transition of γ‐ to β‐phase. In the case of ( the conductivity is not changed by the heating procedure. The activation energies of conduction for at near room temperature are about 7.0 and 9.5 kcal/mole respectively. The crystal structure of the compressed differs from the ideal zinc blende structure. The modified structure has been suggested to be the average one which has silver ions distributed randomly over the ideal position of the ideal zinc blende structure and the four positions surrounding the ideal position.