The nucleation and growth process of extended defects in yttria-stabilized cubic zirconia (8 mol % Y2O3-doped ZrO2) was observed in situ using an ultra-high-voltage electron microscope with varying electron energies (1.25 to 3.0 MeV) and irradiation temperatures (300 to 773 K). Because of differences in mass and threshold displacement energy Ed between anions and cations, two types of dislocation loops—oxygen-type nonstoichiometric dislocation loops and perfect-type dislocation loops—were formed depending on electron energy and irradiation temperature. The intensity distribution of electron flux in the typical electron beam used in this work was found to influence the migration of oxygen interstitials from the center to the peripheral region of the beam, leading to the formation of oxygen-type dislocation loops at the periphery. The role of irradiation temperatures in the nucleation, growth, stabilization, and recovery of defects, such as dislocation loops, is discussed. The threshold displacement energies Ed for Zr and O sublattices were estimated using a well-defined experimental technique and compared with previously reported values. Furthermore, microstructure changes in yttria-stabilized zirconia specimens with 200-MeV Xe ions were examined under electron irradiation. Microstructure change was analyzed in terms of the annihilation and nucleation of point defect clusters at the ion tracks induced by ion irradiation.