Poly(acrylonitrile-co-N-vinyl-2-pyrrolidone)s (PANCNVPs) show excellent biocompatibility. In this work, PANCNVPs with different contents of N-vinyl-2-pyrrolidone (NVP) were fabricated into asymmetric membranes by the phase inversion method. The surface chemical composition of the resultant membranes was determined by Fourier transform infrared spectroscopy-attenuated total reflection. Field emission scanning electron microscopy was used to examine the surface and cross section morphologies of the membranes. It was found that the morphologies hardly change with the increase of NVP content in PANCNVP, while the deionized water flux increases remarkably and the bovine serum albumin (BSA) retention decreases slightly. Experiment of dynamic BSA solution filtration was carried out to evaluate the antifouling properties of the studied membranes. The relative flux reduction of PANCNVP membrane containing 30.9 wt % of NVP is 25.9%, which is far smaller than that of the polyacrylonitrile membrane (68.8%). Results deduce that this improvement comes from the excellent biocompatibility of NVP moieties instead of the hydrophilicity change, because the water contact angles of these membranes fluctuate between 60 and 70. Results from the membranes using poly(N-vinyl-2-pyrrolidone) (PVP) as an additive confirm that, to a certain extent, the PANCNVP membranes show the advantages of antifouling compared with the polyacrylonitrile/PVP blending membrane. (c) 2006 Wiley Periodicals, Inc.