A thermal stable composite membrane was prepared by interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) on poly(phthalazinone ether sulfone ketone) (PPESK) ultrafiltration membrane. Various parameters of the interfacial polymerization were optimized. The surface morphologies of the composite membrane and the substrate were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The membrane obtained at optimized conditions rejected 2000 mg L-1 NaCl solution by 99.0% and the flux was 12.3 L m(-2) h(-1) when tested at 1.2 MPa, 20 degrees C. The rejection of the membrane for ions follows such sequence: Li+ approximate to Na+ approximate to K+ > Ca2+ > Mg2+ > Al3+, SO42- > Cl-. The rejection for organics increased as their molecular weight increased. The permeated flux of 2000 mg L-1 NaCl solution increased from 22.9 to 76.0 L m(-2) h(-1) with stable rejection as the operating temperature increased from 25 to 95 degrees C when the pressure fixed at 1.6 MPa. The membrane demonstrated good thermal stability both in salt solution concentration and wastewater treating processes. The flux decreased less than 3.5 L m(-2) h(-1) during 15 days of high temperature wastewater treatment and the CODCr value of the product water was below requested level. (c) 2005 Elsevier B.V. All rights reserved.