Poly(phthalazinone ether sulfone) (PPES) hollow fiber ultrafiltration (UF) membranes were successfully prepared by the phase inversion method using N-methyl-2-pyrrolidone (NMP)/tetrahydrofuran (THF) as solvents. Ethylene glycol methyl ether (EGME) and diethylene glycol (DegOH) were selected as the non-solvent additives (NSA) to adjust morphologies and separation performances of the PPES membranes. Thermodynamics of the PPES/(NMP/THF)/NSA system was studied by means of the phase separation diagram. Flux of the PPES hollow fibers prepared without additives decreased greatly when the ratio of NMP/THF was lowered in the casting solution, and the rejection of polyethylene glyco14000 (PEG4000) was very high. Introduction of the additives into the casting system significantly changed the membrane performance on rejections of PEGS. When DegOH was used as an additive and the approaching ratio was 0.6 in the casting solution, flux of the membranes prepared from the solvent system NMP/THF (8:2) was 410L/(m(2) h), and the rejection of polyethylene glyco120,000 (PEG20,000) was about 98.3%. When EGME as additive and the approaching ratio as 0.4 with NMP/THF (8:2) used, flux of the membrane was 315L/(m(2) h), and the rejection of polyethylene glycol10,000 (PEG10,000) was about 98.7%. (C) 2009 Elsevier B.V. All rights reserved.