Polymer electrolyte films consisting of polyethylene oxide (PEG), polyacrylonitrile (PAN), LiClO4 and a mixture of ethylene carbonate (EC) and gamma-butyrolactone (BL) were examined in order to obtain the best compromise between high conductivity, homogeneity, dimensional and electrochemical stability. Measurements of electrical conductivity, differential scanning calorimetry and linear sweep voltammetry have been carried out for films of (50-x)PEO-xPAN-7LiClO(4)-43EC/BL and (50-x)PEO-xPAN-12LiClO(4)-38EC/BL with x=10, 20, 30, 40 and 50. When the EO/AN ratio is lower, the PEG-rich crystalline domains are nearly absent. The PEG-PAN blend film is more likely to be a gel-electrolyte than a plasticized PEG-salt electrolyte. The Li+ ions in these films seem to migrate primarily through the solvent domains as in the gel electrolytes. The highest room temperature conductivity of 1.2 x 10(-3) S cm(-1) is found for a film of 10PEO-40PAN-12LiClO(4)-38EC/BL. The beneficial effects of PEO blending with PAN-based electrolytes are in comparable ionic conductivity, better dimensional stability and wider electrochemical stability. (C) 2000 Elsevier Science Ltd. All rights reserved.