The paper contains the results of microstructure and chemical composition analyses of micrograins, which were formed on initial grain boundaries in ZrO2-Y2O3 and ZrO2-Y2O3-MgO systems. It has been found that the micrograins appear in the process of diffusion induced by grain boundary migration (DIGM). The observed processes can be described as both liquid film migration (LFM) and chemically induced grain boundary migration (CIGM). New micrograins had an increased content of Y2O3 and a cubic symmetry. Zirconia-yttria solid solutions with magnesia particulate addition showed an increased amount of migration nuclei and bigger size of new grains. However, no change in the chemical composition of the grains has been detected. The ionic conductivity measurements have shown that the activation energy (E-a) of conductivity at lower temperatures is connected to a DIGM-like process and to the distance of grain boundary migration. In the case of materials with dominating LFM process an increased grain boundary migration distance leads to a lowering of the activation energy of conductivity. Contrary to that, in the materials with dominating CIGM process an increase of migration zone causes increase of E-a values. The data obtained with respect to the type of DIGM process (LFM or CIGM) indicate that the grain boundary conductivity contribution increases with the CIGM distance.