High-density polyethylene (HDPE) hollow fiber membranes were prepared by stretching the melt spun hollow fiber precursors. Slit-shaped pores were successfully developed by cold and hot stretching processes. Annealing before stretching had a great influence on the precursor properties such as orientation, crystallite size and crystallinity. These property changes directly affected the membrane structure, and stretching without annealing failed to make a microporous structure. Take-up speed affected the lamellar thickness and interlamellar amorphous domain size, which in turn determined the pore size. Installation of an air-cooling unit determined the cooling time for crystallization for various take-up speeds. A decrease of cooling time prohibited an increase in orientation, and caused the decrease of crystallite size and crystallinity of the precursor. Take-up speed and annealing conditions were optimized for proper structure formation by stretching. (C) 2008 Elsevier B.V. All rights reserved.