Polymer blend hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and poly (ethylene-co-vinyl alcohol) (EVOH) were used as polymers and diluent was polyethylene glycols (PEG) with the molecular weight of 200. The phase diagrams obtained in the polymer blends system indicated both UCST (upper critical solution temperature) and LCST (lower critical solution temperature) behaviors. For LCST behavior, there were two kinds of phase separations. It was considered that the phase separation occurred at higher temperature was between PVB and EVOH, and that occurred at lower temperature was between polymer and diluent. The addition of EVOH had an eminent effect on the hollow fiber membrane structure and membrane performance. With the increase of EVOH content in the polymer blend system, the membrane became more hydrophilic, and the water permeability became higher due to the enlargement of the pores. The addition of EVOH was also effective to improve the mechanical property of hollow fiber membrane. (c) 2006 Elsevier B.V. All rights reserved.