Superplastic behaviors in various cation doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) were examined. For 1 mol% cation-doping the flow stress of Y-TZP is very dependent on the ionic radii of the doped cations, for instance, smaller cation radii give rise to lower flow stress when comparing the various compositions for the same grain size, strain rate and testing temperature. The altered flow stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrQ. Meanwhile, the strain to failure of the doped zirconia are affected by both ionic radius and valancy of the dopant cations.