We report here our investigation into the ionic conductivity and other electrochemical properties of this micro-phase separation type solid-state electrolyte (SPE). The novel polymer electrolyte has been obtained by swelling an interpenetrating polymer network (IPN) with liquid electrolyte solutions of inorganic lithium salts dissolved in a plasticiser or mixture of plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), gamma-butyrolactone (gamma-BL) and dimethyl carbonate (DMC). The interpenetrating networks are prepared by sequential interpenetration of cross-linked methoxyoligo(oxyethylene)methacrylate (Cr-MOEnM, where n represents number of unit -CH2CH2O-) and cross-linked poly(methylmethacrylate) (PMMA). The IPN electrolytes exhibit conductivities in the range of 4.5x10(-4) to 1.4x10(-3) S cm(-1) at ambient temperature. Cyclic voltammetry of the IPN electrolytes on stainless steel electrode shows electrochemical stability windows of 5.0, 4.2 and 4.0 V vs. Li+/Li for IPN electrolytes with 1 M LiClO4/EC-DMC (1:1 by volume), 1 M LiBF4/gamma-BL and 1 M LiSO3CF3/EC-PC (1:1 by volume), respectively. The impedance of the Li/electrolyte interface for the IPN electrolyte with 1 M LiClO4/EC-DMC under open circuit conditions is found to increase rapidly over the first 30 h and then level off, in contrast to the case for the CrMOEnM network electrolyte (i.e., a network without PMMA) where the impedance increases continuously with time.