It is shown that the increase in conductivity of polycrystalline silver iodide due to its mechanical treatment can be attributed to the presence of metastable defects which are formed on mechanical treatment of AgI. Defects may be annealed by heating with the annealing rate depending on purity of AgI. The temperature dependence of conductivity for purified AgI has two temperature regions with different activation energies : 0.3 and 0.5-0.6 eV at 350-400 K and below 350 K, respectively, which are interpreted in terms of the extrinsic-like conductivity accompanied by the defects ’freezing’ process at lower temperatures. As it will be reported in the following parts of the paper devoted to dielectric and structural studies of mechanically treated AgI, antiphase boundaries formed in beta-gamma polytypes as a result of the treatment are the most probable sources of metastable defects responsible for the conductivity enhancement observed.