Hollow fiber kidney dialysis membranes using linear and hyperbranched polyethersulfone (PES) materials were fabricated in this work by dry-jet wet spinning technique and were post-treated to fine tune their pore structures following open literature approaches. To identify the rooting causes for membranes morphology and performance differences, comprehensive comparisons of the polymer materials, especially their as-spun hollow fiber kidney dialysis membranes were conducted based on their physical, chemical, thermal and theological properties. The most significant differences between the hyperbranched PES material and its linear analogue were identified by its higher molecular weight, wider molecular weight distribution and a much more compact structure. The molecular characteristics of hyperbranched PES led its as-spun membrane with smaller pores, narrower pore size distribution, and a smaller MWCO. In addition, hyperbranched PES bound stronger with the additive PVP and their blend displayed a lower coefficient of thermal expansion (42.16 mu m/degrees C) than that for linear PES (89.08 mu m/degrees C). Both factors led a higher water temperature to tailor the as-spun hyperbranched PES hollow fibers with the pore size and pore size distribution suitable for kidney dialysis application. (C) 2008 Elsevier B.V All rights reserved.