A dozen polyacrylonitrile (PAN)-based polymer electrolytes containing various plasticizers, have shown ionic conductivities higher than 1 x 10 - 3 S cm - 1 at room temperature. In order to explain the high ionic conduction in these systems, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Raman scattering and infrared (IR) spectra have been measured systematically. Based on these results, a mechanism of Li + ion transport in PAN-based polymer electrolytes has been suggested. There are three kinds of Li + ions: one in the gel state of PAN, the other in solid PAN and the third in the plasticizer. The high ionic conduction is mainly caused by the Li + ions in the gel state. These Li + ions are coupled with the C N group in PAN and the C O group in the plasticizer. The Li + ions can jump from one position to the next along a chain, while moving together with the chain.