The results of electrical conductivity measurements on ZrO2:Sc (ScSZ) ceramics as a function of oxygen activity and temperature are presented. The influence of the microstructure on electrical transport is discussed and the experimental data for dense microcrystalline specimens have been compared with those obtained for dense nanocrystalline thin films. From these results the electronic and ionic contribution to the electrical transport has been determined and correlated with microstructure. It has been found that nanocrystalline ScSZ films possess quite different nonstoichiometry compared with that observed for microcrystalline specimens in the fact that the electronic conductivity is enhanced so that it dominates the total conductivity in reducing atmospheres.