Carboxylic poly(ether sulfone) membranes were prepared by a controlled acetylating and surface-oxidating reaction followed by the grafting of bovine serum albumin (BSA) and bovine serum fibrinogen (BFG) onto the surfaces. Attenuated total reflectionFourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Micro BCA Protein Assay Kits confirmed that the proteins were successfully grafted onto the surfaces of the membranes. The protein grafting degrees were measured at different time intervals and under different conditions. The modified membranes showed higher hydrophilicity, lower protein (BSA and BFG) adsorption, and suppressed platelet adhesion values. Because of the binding of calcium ions in blood, the modified membranes showed longer plasma recalcification times, activated partial thromboplastin times, prothrombin times, and whole blood clotting times. The results indicate that the blood compatibility of the poly (ether sulfone) membranes could be improved after surface carboxylic modification and protein immobilization and that the modified membranes could be used in the blood purification field. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012