High-strain-rate superplasticity is attained in a 3-mol%-Y2O3-stabilized tetragonal ZrO2 polycrystal (3Y-TZP) dispersed with 30 vol% MgAl2O4 spinel: tensile elongation at 1823 K reached >300% at strain rates of 1.7 X 10(-2) - 3.3 X 10(-1) s(-1). The flow behavior and the microstructure of this material indicate that the MgAl2O4 dispersion should enhance accommodation processes necessary for grain boundary sliding. Such an effect is assumed to arise from an enhancement of the cation diffusion by the dissolution of Al and Mg ions into the ZrO2 matrix and from stress relaxation due to the dispersed MgAl2O4 grains.