Microporous polypropylene hollow fiber membrane was prepared by the melt spinning and cold-stretching method. In order to measure the porosity of the hollow fiber membrane, bubble point measurement and microscopy of the both sides of a hollow fiber were done, and the area fraction and the volume fraction of micropores were estimated through image analyzer and mercury porosimeter. The bubble point of the of micropores were estimated through image analyzer and mercury porosimeter. The bubble point of the hollow fiber measured in 30%(v/v) aqueous ethanol solution was 1.5kg/cm². Slit-shaped micropores were evenly spread all over the hollow fiber membrane, and parallel to the fiber axis with a stripe pattern. The micropores of the inside and the outside of the hollow fiber membrane have the similar morphology and their area fractions were 30-40%. Pore size distribution was tend to be normal, and the total volume fraction of the micropores was about 52%.