Antifouling ultrafiltration membranes were prepared by polyacrylonitrile-block-polyethylene glycol (PAN-b-PEG) copolymers through immersion precipitation phase inversion method. The effect of copolymer composition and PEG chain length on the structure and property of the block copolymer membranes were investigated. Compared with PAN membranes, PAN-b-PEG copolymer membranes possessed excellent hydrophilic surface due to the enrichment of PEG segments, which was confirmed by X-ray photoelectronic spectroscopy (XPS) and contact angle measurements. SEM images showed these PAN-b-PEG copolymer membranes had a typical asymmetric structure similar with PAN membranes, but the thinner skin layer was helpful for the membrane resistance reduction. The PAN-b-PEG copolymer membranes exhibited better antifouling ability for BSA than PAN membranes. The BSA absorption amount on the copolymer membrane could reduce 45% than that on the PAN membrane, and its irreversible fouling extent could lower 7 times. The hydrophilicity and antifouling ability of the copolymer membranes increased with increasing PEG content in the copolymer. While the chain length of PEG had little effect on the hydrophilicity and antifouling ability of the copolymer membrane. (C) 2011 Elsevier B.V. All rights reserved.