Ultrafiltration (UF) membranes have been prepared successfully from poly (phthalazinone ether sulfone)-bisphenol (PPES-B) by the phase inversion method with N-methyl-2-pyrrolidone (NMP) as solvent. Two types of PPES-B used in this research, contained bisphenol-A unit/phthalazinone unit ratios of 1:1, 1:3, respectively, and were named as PPES-B(1:1) and PPES-B(1:3). Five additives were selected in this study, including butanone (130), ethyl ether (EE), ethyleneglycol monornethylether (EGME), diethylene glycol (DEGC) and polyethylene glycol400 (PEG400). The effects of type and concentration of additives on PPES-B membrane performance and cross-section morphology were investigated in detail. PPES-B(1:1) membranes were compared with PPES-B(1:3) membranes in the membrane performance and cross-section morphology. The resulting membranes can reject PEG with molecular weight of 2000-20,000 Da. And there were two recommendable h) and the rejection of 99% for PEG 10000. and the other exhibited the pure membrane products. One had the pure water flux of 578 kg/(m(2) water flux of 1041 kg/(m(2) h) and the rejection of about 80% for PEG 10000. In addition, the thermal stability of PPES-B(1:3) membrane was also studied. When the operation temperature was raised from 18 degrees C to 95 degrees C. the solution flux increased by nearly 1.4 times with only slight decrease of rejection. (c) 2005 Elsevier B.V. All rights reserved.