The creep behavior of a high-purity tetragonal zirconia polycrystal containing 3 mol% yttria (3Y-TZP) is characterized with a stress exponent of n-2.7 and a grain size exponent of p similar to2.0-3.0 in a high stress region, and with n similar to1.3 and p similar to2.0 in a low stress region. These regions are connected with a transition region with n greater than or equal to5, and accordingly the creep stress-strain rate relationship as a whole exhibits a sigmoidal feature. The apparent activation energy in the high and the low stress regions is the same, 580 kJ/mol, which corresponds to a value reported for lattice diffusion of cations. In the high stress region, evidence of intragranular dislocations revealed by TEM suggests that the motion of intragranular dislocations would contribute to the accommodation process of grain boundary sliding. In the low stress region where such dislocations were not observed, the combination of n similar to1.3 and p similar to2.0 suggests an intervention of lattice diffusion creep.