Conductivity of yttria stabilized zirconia produced from weakly agglomerated nanopowder was investigated by ac impedance spectroscopy. Dense ceramic samples with the grain size from 90 to 800 nm were prepared at the variation of both pressing and sintering conditions. It was found that the bulk conductivity is not affected by grain size, while grain boundary conductivity is dependent on this factor. Observed grain boundary resistance increases with grain size. This relationship is contrary to the previous results obtained for the range from 1 to 18 microm where grain boundary resistance decreased with grain size. Maximum of grain boundary resistance versus ceramics grain size is observed at 450 degrees C for the grain size about 270 nm.