[en] Previous studies on the ceria-gadolinia system have mainly been done on oxides rich in ceria. The purpose of the present work is therefore to establish how the conductivity, density and structure depend on the gadolinia content especially at high doping levels. Five different compositions were examined: Cesub(1-x)Gdsub(x)Osub(2-x/2) with x = 0.1, 0.3, 0.5, 0.7 and 0.9. Oxide powders of these compositions were prepared by homogeneous precipitation of carbonates by hydrolysis of urea followed by calcination in air. Specimens were prepared by pressing and sinterig in air at 1550degC. Conductivity measurements on discs cut from the sintered specimens in the temperature range 400 - 900degC showed that the oxygen-ion conductivity decreases with increasing gadolinia content with a corresponding increase of the activation enthalpy for oxygen-ion migration. A model describing the variation of the theoretical density in this system is presented. From this model the densities of the sintered specimens was found to be in the range 93 - 99% TD. Finally X-ray diffraction on the calcined powders showed that fcc single-phase material exists up to about x = 0.4 after which a bcc phase is formed. (author)