The effect of nanosized Al2O3/ZnO fillers on the interactions in PEO-NaSCN polymer electrolytes has been studied by FT-IR, XRD, and DTA measurements. The experimental results are discussed according to the grain boundary effect, the principle of Lewis acid-base, and epitaxial effect. It is shown that the hard Lewis acid centers on the surface of Al2O3 exhibit strong interactions with ether oxygens in PEO, even with ether oxygens that coordinated to Na+. Therefore, the modes of the interaction of Al2O3 with PEO-NaSCN electrolytes are dependent on the salt content. Al2O3 cannot influence the ionic association in P(EO)(8)NaSCN electrolyte, but do reduce significantly the solvating ability of PEO toward NaSCN in P(EO)(60)NaSCN electrolyte. However, NaSCN in P(EO)(20)NaSCN-30%Al2O3 nanocomposite appears as a state that resembles the situation of NaSCN in PEO amorphous phase. In contrast with Al2O3, the epitaxial effect of ZnO is not found in the interested systems where only weaker interaction is observed between ZnO and ether oxygen, and the modes of interaction of ZnO with PEO-NaSCN electrolytes are hardly related to the salt content. In addition, the soft Lewis acid groups on ZnO surface exhibit stronger complexation with SCN- in PEO-NaSCN electrolytes, and both can form the complex anion ZnO...SCN-.