Nanometric Samaria 20% mol Doped Ceria (SDC20) powders were synthesized by a co-precipitation method. Nano-sized SDC20 powders (crystal size ∼ 15 nm) were obtained by calcination at 600°C. The powders were formed by uniaxial pressure and then sintered. Sintering procedures were led both conventionally, at 1500°C for different sintering times (1, 5, and 10 h), and by fast firing process at different temperatures (1200, 1300, 1400, 1500, and 1600°C for ∼ 0.1 h). Different microstructures were obtained from the different thermal treatments. Electrochemical impedance spectroscopy (EIS) was used to determine total conductivity and to separate bulk and grain boundary impedance contributions. As expected, densification and electrical properties of the conventionally sintered samples showed to be mainly dependent on the average grain size. On the other hand, for the fast fired samples, lattice diffusion mechanism mainly controlled the densification, boundary arrangement and the resulting microstructures at various temperatures. copyright The Electrochemical Society.