A gel polymer electrolyte based on the blend of poly(methyl methaerylate-co-acrylonitrile-co-lithium methacrylate) (PMAML) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was prepared and characterized. The synthesized PMAML were characterized by FTIR and H-1 NMR, respectively, and the surface morphology of the PMAML and PVDF-HFP blend membrane was also observed by scanning electron microscope (SEM). The electrochemical properties of composite electrolyte membranes were studied. The ionic conductivity of the polymer electrolyte composed of 75 wt.% 1 M LiBF4 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 1:1 by weight) was about 2.6 x 10(-3) S cm(-1) at ambient temperature. The electrochemical window of the polymer electrolyte was about 4.6 V determined from the linear sweep voltarnmetry plot. The lithium ion polymer batteries were assembled by sandwiching gel polymer electrolyte between LiCoO2 cathode and mesophase carbon fibre (MPCF) anode. Charge-discharge test results display that lithium ion batteries with these gel polymer electrolytes have good electrochemical performance. (C) 2003 Elsevier Ltd. All rights reserved.