Citric acid, a widely used anticoagulant, was grafted onto polyurethane through a two-step solution polymerization. The novel synthesized polymer can be directly blended with polyethersulfone (PES) to prepare membranes. The modified membranes showed lower protein (bovine serum albumin, BSA; bovine serum fibrinogen, BFG) adsorption and suppressed platelet adhesion. Due to the binding of calcium ions in blood, the modified membranes effectively prolonged the activated partial thromboplastin time (APTT), prothrombin time (PT), plasma recalcification time (PRT) and the whole blood clotting time (WBCT). Furthermore, the modified membranes showed good cytocompatibility, and the surfaces promoted hepatocyte adhesion and proliferation compared to pure PES membrane. These results indicated that the surface modification by blending citric acid grafted polyurethane provided practical application of the membranes with good biocompatibility, especially the anticoagulant property; and the membranes could be used in blood purification fields, such as hemodialysis and bioaritificial liver assist devices. (C) 2012 Elsevier B.V. All rights reserved.