Effects of the cooling methods on the structure of polypropylene fibers are studied. In this study, the effect of two different cooling methods, air cooling and water quenching, were studied. Since the cooling rate in the water-quenching method is higher than that by air-cooling, water-quenched fibers exhibited smectic phase, while air-cooled fibers exhibited stable monoclinic phase. Structure and properties of the hollow fibers are compared with those of circular fibers of the same cross-sectional area. The cooling rate for the hollow fibers is greater than that for the circular shape fibers due to increased surface area. Both the temperature of tan$delta$ maximum($T_{tan{deltamax}}$.) and the activation energy of the chain mobility for the hollow fibers are greater than those of circular-shaped fibers. The structural changes during the drawing process are also investigated. During the drawing process, the crystalline phase of air-cooled fibers did not change much, but the smectic phase in water-quenched fibers was transformed into the monoclinic phase.