In order to develop polymer electrolyte for lithium ion batteries, highly porous P(VDF-HFP) membranes were prepared by using phase inversion method, then they were immerged in 1molkg−1 solution of LiClO4-EC/PC(1:1) to form porous polymer electrolytes. Conductivity of the polymer electrolytes was found to be as high as 10−3 Scm−1. Structures of the porous membranes were observed with SEM. Porous membranes with different structure, porosity and pore diameter were prepared by changing the processing conditions. There are two kinds of typical structure, one is honeycomb-like (type I), and the other is network-like (type II). Membrane structures were found to be important to the performance of the porous polymer electrolytes. Small pore diameter with narrow distribution is needed to prevent solution leakage and high porosity is needed to achieve high conductivity. The type II membranes can meet the requirements. The model lithium ion batteries made of the resulting porous polymer electrolytes have good cycleablity.