High energetic milling of the corresponding oxides and carbonates mixture was employed to obtain highly dense ceramics with Ce0.80Sm0.20−x Ca x O1.9 (x =0, 0.02) compositions at low sintering temperature. After 17h of milling, the samarium and calcium have entered in the ceria fluorite-type structure, indicating that the mechanosynthesis of the material has occurred. Densities in the order of 97–98% were obtained at temperatures as low as 1250–1300°C in a single thermal treatment. Besides, the addition of Ca is shown as a clear aid to sinter high-density ceramics with improved grain size for the increase of the ionic conductivity. The high homogeneity of the mixture allows Ca not only to partially incorporate to the structure, but also to react to the glassy siliceous phase located at the grain boundary. This effective cleaning process, together with the additional grain growth promoted by Ca doping, increases the grain boundary conductivity, and thus, the total conductivity of the ceramics. The influence of the microstructure on the electrical properties of the ceramics is discussed.