Li+-ion and Na+-ion transfer at interfaces composed of inorganic solid electrolytes and polymer or organic liquid electrolytes were compared. La0.55Li0.35TiO3 and Na3Zr1.88Y0.12Si2PO12, which axe conductive for Li+ and Na+, were selected for use as inorganic solid electrolytes. PC solution and PEO-based polymer electrolytes were added to Li salt or Na salt to give ionic conductivity. Using these electrolytes, solid electrolyte/liquid electrolyte or solid electrolyte/polymer electrolyte interfaces were constructed. The resistivities of Li+ or Na+ transfer through these interfaces were estimated based on the results of ac impedance measurements. In both solid/liquid and solid/polymer systems, the activation energies of Na+-ion transfer at the interface were smaller than those of Li+-ion. The Lewis acidity of both ions, Li+ and Na+, clearly explains this difference and supports the idea that the interaction between ion and solvents plays a major role in interfacial ion-transfer processes. (c) 2005 Elsevier B.V. All rights reserved.