Polyvinyl butyral (PVB) hollow fiber membranes were prepared via wet-spinning method using polyvinylpyrrolidone (PVP) as additive. The effects of PVP and PVB concentration, bore fluid composition on the membrane formation were investigated by viscosity, light transmission, scanning electron microscopy (SEM) and ultrafiltration respectively. Results revealed that PVB and PVP have a good miscibility. Addition of PVP mainly changed the kinetic property of the dope, such as the increased viscosity, the delayed demixing, etc. The cross-sections of the resulting membranes showed a similar asymmetric structure. Ultrafiltration showed that the rejection of membrane increased, but the flux firstly increased then decreased with an increase in PVP concentration. The low PVB concentration in the dope caused a loose cross-sectional morphology, which improved the water flux of membrane. Moreover notable difference occurred at the internal surface of PVB hollow fiber membrane when N,N-dimethulacetamide (DMAc) was added to the bore fluid. As a result, membrane exhibited a high flux with no significant change in retention performance. (C) 2011 Elsevier B.V. All rights reserved.