Abstract A novel thin-film composite (TFC) membrane for nanofiltration (NF) was developed by the interfacial polymerization of triethanolamine (TEOA) and trimesoyl chloride (TMC) on the polysulfone (PSf) supporting membrane. The active surface of the membrane was characterized by using FT-IR, XPS and SEM. The performance of TFC membrane was optimized by studying the preparation parameters, such as the reaction time of polymerization, pH of aqueous phase and the concentration of reactive monomers. It is found that the membrane performance is related to the changes of the monomer content in the aqueous phase rather than in the organic phase. Furthermore, the nanofiltration properties of the TFC membrane were tested by examining the separating performance of various salts at 0.6 MPa operating pressure. The rejection to different salt solutions decreased as per the order of Na 2SO 4 (82.2%), MgSO 4 (76.5%), NaCl (42.2%) and MgCl 2 (23%). Also, streaming potential tests indicated that isoelectric point of the TFC membrane is between pH 4 and 5. Moreover, the investigation of the flux for NaCl solution at different pH showed that the polyester NF composite membrane is also particularly suitable for treating acidic feeds: the flux increased from 8.4 to 11.5 L/m 2 h when pH of the feed decreased from 9 to 3. Additionally, the TFC membrane exhibits good long-term stability.