Starting from a sinter reactive powder prepared by a gel precipitation technique, dense, ultra-fine grained (100–200 nm) yttria stabilized tetragonal zirconia ceramics were obtained by sinter forging at a temperature of 1100 °C or by pressureless sintering at 1150 °C. The pressureless sintered compacts were subjected to further heat treatments at temperatures of 1250–1450 °C or compressive deformation at 1250 °C under uniaxial stresses of 20–100 MPa. The obtained samples were characterized mainly by impedance spectroscopy. After compressive deformation a decrease in grain boundary resistivity was found which increased with applied stress. This can be interpreted in terms of a decrease in impurity segregation and a partial removal by compressive deformation of a poorly conducting amorphous film around the grains. It was also found that the grain boundary resistivity of samples sintered at 1150 °C could be considerably reduced by further pressureless heat treatments at temperatures above 1250 °C. This effect is probably owing to dewetting of the grain boundary and dissolution of grain boundary impurities into the bulk of the grains.