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 tons : 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.