Polypropylene (PP) microporous membranes were successfully prepared by swift heavy ion irradiation and track-etching. Polypropylene foils were irradiated with 197Au ions of kinetic energy 11.4 MeV·u-1 (total energy of 2245.8 MeV) and fluence 1×108 ions·cm-2 at normal incidence. The damaged regions produced by the ld ions along the trajectories were etched in H2SO4 and K2Cr2O7 solutions leading to the formation of cylindrical pores in the membranes. The pore diameters of the PP microporous membranes increased from 380 to 1610 nm as the etching time increased from 5 to 30 min. The surface and cross-section morphologies of the porous membranes were characterized by scanning electron microscopy (SEM). The micropores in the membranes were found to be cylindrical in shape, homogeneous in distribution, and equal in size. Some mathematical relations of the porosity of the PP microporous membranes were established by analytic derivation. The microporous membranes were used in lithium-ion batteries to measure their properties as separators. The electrical conductivity of the porous membrane immersed in liquid electrolyte was found to be comparable to that of commercial separators by electrochemical impedance spectroscopy (EIS). The results showed that the porosity and electrical conductivity were dependent on the ion fluence and etching time. By adjusting these two factors, microporous membranes with od porosity and electrical conductivity were made that met the requirements for commercial use.