Ionic-liquid-containing polymer films were prepared by swelling poly(ethylene glycol)-based networked polymers having lithium salt structures with an ionic liquid, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMImFSI), or with an EMImFSI solution of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Their fundamental physical properties were investigated. The networked polymer films having lithium salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3-glycidyloxypropanesulfonate or lithium 3-(glycidyloxypropanesulfonyl)(trifluoromethanesulfonyl) imide with poly(ethylene glycol) bis(3-aminopropyl) terminated. The obtained ionic-liquid-containing films were flexible and self-standing. They showed high ionic conductivity at room temperature, 1.16-2.09 S/m for samples without LiTFSI and 0.29-0.43 S/m for those with 10 wt % LiTFSI. Their thermal decomposition temperature was above 220 degrees C, and melting temperature of the ionic liquid incorporated in the film was around -16 degrees C. They exhibited high safety due to good nonflammability of the ionic liquid. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3582-3587, 2011