The poly(vinyl butyral) (PVB) hollow fiber ultrafiltration membranes were prepared using three polyvinylpyrrolidones (PVPs) with different molecular weight (M-w) as additives by wet spinning method. Effects of PVP M-w on the coagulation process, morphologies and properties of the as-spun PVB membranes were researched with PVP M-w and bore liquid. The results illustrate that the PVB/PVP/N-methyl-2-pyrrolidone (NMP) dopes have an instantaneous demixing mechanism and the demixing rate declines with the rise of PVP M-w. The fibers fabricated with both two bore liquids have an asymmetrical single finger-like structure. Nevertheless, the fibers fabricated with 90 wt.% NMP aqueous solution as bore liquid form slightly longer single finger-like macrovoids and larger pores in the inner surfaces. The PVB membranes containing PVP with lower M-w and with 90 wt.% NMP aqueous solution as bore liquid have higher hydraulic permeability (J(w)) than those containing PVP with higher M-w and with 50 wt.% ethanol aqueous solution as bore liquid. The highest J(w) value 135.1 L M-2 H-1 bar(-1) is obtained for the PVB membrane with a MWCO of 111.7 kDa. The break strain, elongation ratio and Young's modulus values of the fabricated fibers increase when the PVP Mw increases. The fibers with 90 wt.% NMP aqueous solution as bore liquid have lower mechanical properties than those with 50 wt.% ethanol aqueous solution as bore liquid. (c) 2013 Elsevier B.V. All rights reserved.