Asymmetric membranes fabricated from poly(acrylonitrile-co-maleic acid) (PANCMA) were immobilized with biomacromolecules to improve their surface biocompatibility. Dual-layer biomimetic membranes were prepared by the reaction of carboxyl groups on the PANCMA membrane surface with chitosan and/or gelatin in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. These surface-modified membranes were analyzed by X-ray photoelectron spectroscopy to confirm the biomacromolecules immobilization. Morphological changes on the surface and in the cross-section of the membranes were characterized by scanning electron microscopy and atomic force microscopy. No obvious affection was observed on the sponge-like structure of the membrane bulk while the roughness of the membrane surface increased after the biomacromolecules immobilization. The surface hydrophilicity and biocompatibility of the original and the dual-layer biomimetic membranes were investigated by water contact angle and platelet adhesion measurements. It was found that, after the immobilization of chitosan and/or gelatin, water contact angle on the membrane surface decreased, indicating the improvement of surface hydrophilicity. The amount of adhered platelet on the dual-layer biomimetic membrane was much less than those on the corresponding PANCMA membrane. Furthermore, relative high permeation fluxes of water and protein solution were obtained for the dual-layer biomimetic membranes. All these results demonstrate that both the surface biocompatibility and the filtration performance of PANCMA membrane can be improved by the described approach to fabricate into dual-layer membrane possessing a biomimetic surface. (c) 2005 Elsevier B.V. All rights reserved.