Poly(vinyl butyral) (PVB)/Pluronic F127 blend hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Polyethylene glycol (PEG) was used as diluent, the effects of diluent molecular weight on the performance of hydrophilic poly(vinyl butyral)/Pluronic F127 blend hollow fiber membrane were investigated. Although the addition of Pluronic F127 to PVB/PEG system led to the decrease of the cloud point, the reduction of cloud point was different as to different molecular weight of PEG. Light scattering results show that the initial interphase periodic distance formed from the phase separation of PVB/Pluronic F127/PEG600 system was smaller than that of PVB/Pluronic F127/PEG200 system and its growth rate was also lower in the former system in cooling process of the PVB/Pluronic F127 solution. In addition, the properties of the PVB/Pluronic F127 blend hollow fiber membranes prepared with different molecular weight of PEG were investigated, the PVB/Pluronic F127 blend hollow fiber membrane prepared with diluent PEG600 has greater breaking strength, elongation and rejection, while the membrane prepared with diluent PEG200 has greater tensile strength and water permeability. (C) 2009 Elsevier B.V. All rights reserved.