Two kinds of composite, based on poly(ethylene oxide) (PEO) and a mineral saponite, were prepared and their thermal behavior, phase composition, microstructure and electrical properties were investigated. The results showed that PEO easily intercalates to the interlayer of saponite, replaces the interlayer water molecules, and acts as medium for lithium ions conduction. PEO-intercalated saponite exhibited conductivity as high as 4.1 x 10(-3) S cm(-1), a lithium ion transference number of 0.99 at 25degreesC and conductivity activation energy of 0.14 ev. Appropriate amounts of intercalated PEO in the interlayer of saponite is important to an ideal ionic conductivity. The PEO-intercalated saponite is thermally stable below 350 degreesC. In addition, a PEO-based composite with lithium saponite as filler showed a homogeneous morphology and combined properties of individual PEO and saponite. The PEO-intercalated saponite could be considered as a good candidate as filler for lithium conductive polymer electrolyte. (C) 2003 Elsevier Science B.V. All rights reserved.