This paper describes the fabrication and performance of microporous gel electrolyte (MGE) Li-ion batteries. The MGE battery was prepared through three steps: (1) making microporous polymer membrane as battery separator by the phase-inversion method, (2) making the battery assembly and activating it with liquid electrolyte, and (3) forming MGE in situ by warming the battery. Depending on liquid electrolyte uptake and warming conditions of the microporous membrane, the resulting MGE may contain three phases: liquid electrolyte, gel electrolyte, and polymer matrix. Therefore, the MGE combines many advantages such as high ionic conductivity, good adhesion to the electrodes, and good mechanical strength. In this work, we used poly(acrylonitrile-methyl methacrylate) (AMMA, AN:MMA=94:6) as the polymer matrix, and a solution of 1.0 m LiBF4 dissolved in a 1:3 (wt.) mixture of ethylene carbonate (EC) and gamma-butyrolactone (GBL) as the liquid electrolyte. Typically, an MGE gelled with 390 wt.% of liquid electrolyte vs. the dried membrane has an ionic conductivity of 2.2 mS/cm at 20 degreesC and the resulting Li-ion battery shows good cycling performance. Published by Elsevier B.V.