Abstract: In the present paper a polydispersed iodobromide photographic emulsion (iodide content 6 mol percent) was divided into nine bunch emulsions with fine,middle and,coarse grains by means of enzymatic treatment. The ionic conductivity of the silver ha-lide microcrystals of each bunch was measured at different temperatures. The ionic conduction activation energy and the surface potential were calculated. It was found that there is a significant difference among different bunches in ionic conduction. The activation energy increases from 0.30 eV to 0.41eV,with decreasing iodide content,meanwhile,the surface potential becomes more and more positive and the interstitial silver ions formation energy becomes higher and higher. The effects of above-mentioned differences on the sensitometric characteristics of different bunches were discussed.