Copoly(phthalazinone biphenyl ether sulfone) (PPBES) ultrafiltration (UF) membrane with low molecular weight cut-off (MWCO) possesses excellent thermal resistance and it is suitable to be utilized in dye wastewater treatment at high temperature. The rejection of polyethylene glycol (PEG1000) of the membrane was 100% while the flux was 232 L/m(2) h at 20 degrees C and 0.2 MPa. It was showed that the rejections of NaCl and Na(2)SO(4) were both 0%. The rejections of Congo Red (Direct Dye), Sulfur Black B (Sulfur Dye) and Gentian Violet (Anionic Dye) were all 100% while the rejections of C. I. Reactive Yellow 86 (Reactive Dye), C. I. Disperse Red 73 (Disperse Dye) and Acid Chrome Blue K (Cationic Dye) were 79%, 54% and 43%, respectively. The fluxes of the membrane during treatment were all higher than 87 L/m(2) h at 20 degrees C and 0.2 MPa except for C. I. Disperse Red 73. Effect of inorganic salt concentration on membrane performance was investigated. Thermal resistance of the membrane was also evaluated with Sulfur Black B. It was found that the flux increased 4.5 times while the rejection did not decline when the operation temperature was raised from 20 degrees C to 95 degrees C. The membrane ran 20 h at 90 degrees C without the membrane performance decline which showed that the membrane had good thermal resistance. (C) 2010 Elsevier B.V. All rights reserved.