A new type of solid polymer electrolyte (SPE) was prepared by sequential interpenetration of cross-linked methoxyoligo (oxyethylene) methacrylate (MOEnM) and poly(methyl methacrylate) (PMMA). When the interpenetrating polymer networks (IPNs) were swollen with liquid electrolyte solutions, they showed structures that were between the chemically cross-linked gel SPEs and the porous SPE. They could swell/hold much more electrolyte solution than the porous SPE. The electrolytes exhibited ionic conductivities in the order of 10(-3) S cm(-1) at 25 degreesC, and could be useful in many practical electrochemical devices. (C) 2001 Elsevier Science Ltd. All rights reserved.