Polypropylene hollow fiber was prepared through the melt spinning apparatus to which a tube-in-orifice type nozzle was fixed, and then annealing, drawing and heat treatment processes were followed to give it microporosity. The effects of the spinning conditions and the post-treatment conditions on the microporosity were investigated by the observation of the hollow fiber membrane surfaces with scanning electron microscope and the bubble point test method. The porosity was good in the hollow fibers spun at the nozzle temperature range of 180∼200℃, and increased with increasing spinning speed and increasing draft ratio. Annealing was carried out at the temperature range of 120∼ 150℃ to enhance the crystallinity of the hollow fiber. The porosity was excellent with 100% drawing in the case of the single drawing, and augmented with the multiplicity of drawings and heat treatments. The formed pores took the shape of the slits which were 0.3μm tong and 0.05∼0.1μm wide in the axial direction of the hollow fiber.