Sulfonated polyetherimide/polyetherimide (SPEI/PEI) ultrafiltration (UF) hollow fiber membranes were prepared with phase inversion method and SPEI was used as a polymer additive. Scanning electron microscope (SEM) study revealed that the addition of SPEI could induce the formation of nodular structure and suppress the formation of finger-like macrovoids. With the increase of air gap distance, it was found that the micropores were formed in the outer fiber surface and the pore size increased accordingly. On the other hand, the pure water flux of the membrane reached a maximum and then decreased while the solute retention decreased at first and leveled off at longer air gap. Through bovine serum albumin (BSA) solution filtration test. it was found that the use of SPEI in the blend membranes increased its hydrophilicity. When SPEI with ion exchange capacity (IEC) of 2.88 mmol/g was blended with PEI by 15/85 weight ratio, 75% of the membrane flux reduction in the BSA solution (pH = 8.0) filtration process was caused by reversible BSA adsorption, compared with 32% for PEI membrane. Increasing the pH value of the BSA solution, the membrane fouling tendency reduced and the reversible flux reduction ratio increased. (C) 2003 Elsevier Science B.V. All rights reserved.