This work investigates the ionic conductivity of nano-sized samaria-doped ceria (SDC), which is often deposited in the electrodes of solid oxide fuel cells to enhance their electrochemical performance by extending the three-phase boundary (TPB) length. The SDC nano-particles are fabricated via an ion impregnation/infiltration method using porous ceria as the backbone and samarium-cerium nitrate solution as the precursor. The apparent conductivity, which is determined with electrochemical impedance spectroscopy, increases with SDC loading and reaches 8.40 x 10(-4) Scm(-1) at 700 degrees C for the loading of 25.1 wt.%. A model is developed to calculate the conductivity of the impregnated phase, which has a porosity of 50.4%. The nano-sized SDC conductivity at 700 degrees C is 9.82 x 10(-3) Scm(-1), lower than 2.09 x 10(-2) Scm(-1) for the bulk SDC prepared from the same precursor. Considering the Bruggeman factor, the conductivity of a dense impregnated SDC is estimated to be 5.88 x 10(-2) Scm(-1), higher than the bulk material. The impedance for the impregnated SDC is characterized by much smaller grain-boundary contribution than the grain-interior, which is quite different with the bulk SOC. (C) 2014 Elsevier Ltd. All rights reserved.