Polymer-inorganic nanocomposite films of PEO-ZnO and PEO-ZnO-LiClO4, where PEO stands for poly(ethylene oxide), have been prepared through a film-casting method. Interactions between PEO (MW = 600 000) and ZnO nanoparticles (average size 3.5 nm, with acetate groups on the surface) decrease the photoluminescence intensity of the PEO film to a great extent. These interactions, which are also manifested by the X-ray diffraction, depend on the concentration and the aggregation of the ZnO nanoparticles in the PEO-ZnO films. The cooperative effect of PEO and LiClO4 changes the unidentate coordination mode of the acetate groups with zinc into three coexisting modes: unidentate, bidentate, and bridging, suggesting that PEO segments, lithium ions, and the acetate groups on ZnO nanoparticle surface form cross-linking structures. Such cross-linking structures, on one hand, reduce Li+ClO4- ion pairs to release more free ions as charge carriers in the PEO-ZnO-LiClO4 film and, on the other, decrease the film crystallinity to produce more amorphous regions for charge carriers to transfer, and finally enhance the conductivity of the film.