In situ free radical polymerization of compatible vinyl monomers (methyl methacrylate, MMA) in a room temperature ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMIPF6), obtained a novel series of gel polymer electrolytes (GPEs) with high ionic conductivity. The resulting polymer gels were flexible, transparent and high conductive films. Their glass transition temperatures decreased with increasing mass fraction of BMIPF6 and behaved as a completely compatible binary system. Analysis of FT-IR spectra showed that there existed an interaction between BMIPF6 and PMMA polymer matrix in the GPEs. The temperature dependence of the ionic conductivity of the polymer electrolyte films followed the Vogel-Tamman-Fulcher (VTF) equation, and the ionic conductivity at ambient temperature reached a value close to 10(-3) S cm(-1). Then the performance of capacitors applying the GPEs was determined by cyclic voltammetry, impedance spectroscopy and galvanostatic charging and discharging. (c) 2006 Elsevier B.V. All rights reserved.