Abstract: The present invention relates to a method of making a polymeric porous separation membrane for a lithium ion polymer battery, the method comprising: providing a porous polyolefin membrane and a polymer solution of the concentration of 1–20 weight % in an organic solvent fabricated by dissolving in an organic solvent a polymer compound that is stable in an electrolyte containing a lithium salt and can be gelled in the electrolyte, at the temperature of 10–40° C.; and fabricating a polymeric porous separation membrane by coating the polymeric porous polyolefin membrane with the polymer solution. Thus, the porous separation membrane for a lithium ion polymer battery is fabricated by using the polymer solution fabricated at the low temperatures of 10–40° C., and the size of the pores of the coated is proper, so that the containing capacity of the electrolyte and the ion conductivity are good. Further gelling at low pressure is enabled and cohesive force to the electrodes is improved.