Fabrication of polysulfone hollow-fiber microfiltration membranes through non-solvent induced phase separation (NIPS) by dry-wet spinning was studied. For all sample preparations, we used N-methylpyrrolidone (NMP) as solvent, polyethylene glycol (PEG) as additive, aqueous NMP solution as bore liquid, and water as coagulation bath. Particular focus was placed on the influence of PEG molecular weight (Mw) on membrane structure. Characterization of the obtained membranes was performed by measuring pure water permeate flux, tensile strength, and tensile elongation at break, and by analyzing scanning electron microscope (SEM) images of hollow-fiber cross-sections, outer surfaces, and inner surfaces. Dope viscosity increased sharply as PEG Mw was raised to 20,000 or higher, as did water permeate flux. SEM image analysis revealed that outer-surface pore size increased with PEG Mw. Morphology of the inner surface transformed markedly as PEG Mw was raised from 6000 to 20,000. (c) 2008 Elsevier B.V. All rights reserved.