Cu6PS5I superionic ceramics were prepared from nanocrystalline powder, obtained by ball milling. From the structural investigations the average grain sizes of nanocrystalline powders were determined. Electrical conductivity measurements were carried out in the temperature interval 300-400 K and in the range of frequencies 10 Hz-3 GHz. The temperature and frequency dependences of electrical conductivity were analyzed. The influence of grain size effect on the electrical conductivity in Cu6PS5I superionic ceramics was studied. (C) 2013 Elsevier B.V. All rights reserved.