An improved process to prepare high separation performance polyamide (PA)/polyvinylidene fluoride (PVDF) hollow fiber composite nanofiltration (NF) membranes was presented. Conventional interfacial polymerization process to prepare composite NF membranes was done through submerging the support membrane in aqueous phase followed by in oil phase. The improved interfacial polymerization process was done by submerging the membrane into aqueous phase again after the conventional process. The experiment was done to prepare PA NF membrane on PVDF hollow fiber support membrane. Results showed that the membrane prepared through this improved process had better separation performance. Using this improved process, membrane structures were improved and the rejections of PA/PVDF hollow fiber composite NF membranes for Na2SO4, MgCl2, KCl, NaCl, PEG600 and PEG 1000 were 92.3%, 7.0%, 9.5%, 14.2%, 88.4% and 89.3%, respectively. (c) 2007 Elsevier B.V. All rights reserved.