The crystal structure of compositionally homogeneous, nanocrystalline ZrO2 - X mol% Y2O3 (X = 2.8, 4, 5, 6, 7, 8, 9, 10, 11, and 12) powders synthesized by a nitrate-citrate gel-combustion process has been studied by X-ray diffraction. By applying the Rietveld method, it was found that all the powders presented the tetragonal phase (P4(2)/nmc space group). The axial ratio c/a(f) decreased with increasing Y2O3 content and became almost unity at 9 mol% Y2O3. However, powders in the compositional range of ZrO2 - 9 to 12 mol% Y2O3 exhibited the oxygen atoms displaced from their ideal sites of the cubic phase along the c axis, which is known as the t"-form of the tetragonal phase. A conjunct analysis of crystallite size and microstrain of all the powders is also presented.