Nanosized polycrystalline samples of (Er1-uGdu)(2)O-3 (0 less than or equal to u less than or equal to 1.0) were synthesized by a sol-gel technique. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range of u. The Er3+ and Gd3+ ions were randomly distributed over two cationic sites, 8b and 24d, in the space group Ia (3) over bar (206) in all refined structures. The lattice parameter was found to vary non-linearly with the composition (u). The average microstrain and average crystallite size have been calculated from the Williamson-Hall plots for each sample. The average size ranges from 50 to 70 nm, and the microstrain from 0.4 to 1.7%.