A new kind of microporous polymeric electrolytes was prepared from microemulsion polymerization of the system containing acrylonitrile (AN), 4-vinylbenzenesulfonic acid lithium salt (VBSLi), ethylene glycol dimethacrylate (EGDMA), omega-methoxy poly(ethyleneoxy)(40) undecyl-alpha-methacrylate (C-1-PEO-C-11-MA-40), and water. The polymerized-microemulsion solids or membranes have open-cell porous microstructures. The water content in membranes can readily be-exchanged with many organic solvents such as gamma-butyrolactone (BL), a mixture of ethylene carbonate(EC) and dimethyl carbonate (DMC) or propylene carbonate (PC) and EC. The membranes can also be filled with electrolyte solutions such as 1M LiBF4/BL, 1M LiSO3CF3/PC-EC, or 1M LiClO4/EC-DMC to form polymeric composite electrolytes. Such composite electrolytes, exhibiting ionic conductivities in the area of 10(-3) S cm(-1) (25 degrees C), may be used in many electrochemical devices.