Ce0.8Sm0.2O2-delta/Al2O3 (SDC/AO) multilayered thin-film electrolytes have been prepared using the radio frequency (RF) magnetron sputtering. The structures and electrical properties of the heterostructured multilayers have been systematically investigated with respect to the layer number. It is found that the ionic conductivity of multilayer structured SDC/AO solid electrolyte is enhanced by nearly 5 times than that of single-layered SDC film, indicating a positive interfacial conduction contribution and a much higher interfacial conductivity than that of the SDC phase. It is estimated that the high interfacial conductivity is mainly attributed to the highly-disordered microstructures with structural defects in interfacial regions which provide fast conducting pathways. These results suggest that a rational design of the interfaces can readily enhance the ionic conductivity of multilayered heterostructure electrolytes, which might subsequently improve the performance of electrochemical devices. (C) 2015 Elsevier Ltd. All rights reserved.