In this study, the polypropylene (PP) membrane with high porosity was prepared by a thermally induced phase separation (TIPS) process in supercritical CO₂. PP resin was blended with camphene and the mixture ans melted at 150 ℃. The melted mixture of PP and camphene was placed between two glass plates and suddenly cooled in a 10 ℃ water. The camphene contained in the membrane was extracted out in supercritical CO₂. Therefore, the dried PP membranes with a high porosity were obtained and they had a sponge structure. Their porosity decreased and tensile stress increased with an increasing PP concentration. Pressure, temperature, and extraction time had an effect on the average pore size and pore structure of the PP membrane.