Poly(vinylidene fluoride) (PVDF) hollow fiber membranes were prepared by thermally induced phase separation (TIPS) using diluent mixtures of dibutyl phthalate (DBP) and di(2-ethylhexyl) plithalate (DEHP). Liquid paraffin, which is a non-solvent for PVDF but a solvent for diluent mixtures, was used as bore liquid to make a lumen of the hollow fiber for purpose of replacement of the droplets formed near the inner surface via liquid-liquid phase separation by that and formation of larger pores at the inner surface of the hollow fiber. The membrane formation mechanism for different structures of hollow fiber membranes was proposed and the effect of membrane structure on the performance of membranes was The experimental results of the water permeability and the solute rejection were attributed to both the pore size at the surface and the pore structure in the bulk of membrane. (c) 2008 Elsevier B.V. All rights reserved.