A systematic study of the influence of the rare-earth (Sc, Yb, Y, Gd, Sm) dopant content and the ionic radius on the structural changes was undertaken on nanocrystalline-doped zirconia ceramics, which present the same microstructure. Tetragonal single-phased ceramics which were prepared by sintering of nano-powders obtained by spray pyrolysis at 1500 degreesC for 2 It in air, are characterized by an average grain size as low as 60 nm. Their densities are about 96% of the theoretical values. A good homogeneity in composition and in grain size was obtained for all samples. This exceptionally low grain growth during the sintering was related to the high purity of the materials and also to the morphology of the powders. Tetragonal solid solution domains were determined from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), and Raman spectrometry measurements. The size of the solid solution domain depends on the dopant ionic radius and on the grain size.