Different phases from the ZrO2-Y2O3 system corresponding to 8, 10, 14, 21, 32, and 37 mol % Y2O3, prepared by quenching from high temperature, have been studied by selected area electron diffraction (SAED) and high-resolution electron microscopy (HRTEM). The results of the 8 and 10 mol% Y2O3 are consistent with a crystal microstructure of three kind of domains of the t or t' phase with the c axes oriented along three mutually perpendicular directions and small displacements of the cations (Zr and Y) from their ideal crystallographic positions. The materials with higher dopant concentration show a modulated fluorite-type structure due to partial or short-range ordering of the oxygen vacancies related to a pyrochlore-type and/or C-type crystal structures.