Polysulfone (PSf) asymmetric hollow-fiber membranes, which have a dense outer layer but a loose inner layer, were tentatively fabricated by coextrusion through a triple-orifice spinneret and a dry/wet-phase inversion process. Two simple polymer dopes were tailored, respectively, for the dense outer layer and the porous inner layer according to the principles of the phase-inversion process. By adjusting the ratio of the inner/outer extrusion rate, the hollow-fiber membranes with various thicknesses of outer layers were achieved. The morphology of the hollow-fiber membranes was exhibited and the processing conditions and the water permeability of the membrane were investigated. (C) 2004 Wiley Periodicals, Inc.