The conduction mechanism of gel electrolyte system consisting of poly(ethylene oxide) branched poly(methyl methacrylate) (PEO-PMA) matrix and ionic liquid containing lithium salt has been investigated. The kinetics of ion conduction and the mobility of lithium ion are different by the kind of ionic liquid; 1-ethyl-3-methyl imidazolium bis(trifluoromethane sulfone)imide (EMITFSI) or hexyltrimethyl ammonium bis(trifluoromethane sulfone)imide (HTMATFSI). Lithium ion exhibits a significant contribution for ion conduction in the gel electrolyte containing HTMATFSI In contrast, the mobility of lithium ion is not obvious in the gel electrolyte containing EMITFSI. Such difference is considered to originate from the difference in 'miscibility' of polymer component in ionic liquid. (C) 2007 Elsevier B.V. All rights reserved.