To improve the electrical conductivity of LiClO4-poly(ethylene oxide) (PEO) complex, nonconductive polyaniline (NPANI) was employed as an additive. The electrical conductivity of the PEO-LiClO4-NPANI electrolyte was at least ten times that of the original PEO-LiClO4 electrolyte. The amine and/or imine nitrogen atoms in the NPANI polymer chain as well as the oxygen atoms in the PEO polymer chain attracted the Li+ ions, and ion-dipole interaction occurred. The interaction enhanced the mobility of the ClO4- ions. The positively charged nitrogens were electronically stabilized in the entire polymer chain because NPANI had conjugated pi electrons. The mechanism is unique and different from those of other polymer additives. It is the very first example in which NPANI was employed as the additive for the PEO solid electrolyte and in which NPANI was found to be an effective additive. In addition, the NPANI addition hardly affected the physical properties of the PEO matrix such as the glass transition temperature and the melting temperature.