A new type of thin-film nanofibrous composite membrane (TFNC) for nanofiltration (NF), prepared by interfacial polymerization (IP) of piperazine (PIP) using ionic liquids (IL) was demonstrated. A comparison was first made to illustrate the advantage of using highly porous electrospun PES nanofibrous scaffold versus typical ultrafiltration (UF) membrane as the support for the PIP-based polyamide barrier layer. Two different ILs: 1-octyl-3-methylimidazolium chloride (OMIC) and 1-butyl-3-methyl-imidazolium chloride (BMIC), were incorporated in interfacial polymerization to adjust the permeation flux and salt rejection ratio (MgSO(4) and NaCl); the results were also compared with those of commercial NF membranes (i.e. NF-90 and NF-270 from Dow FILMTEC). The existence of non-reactive IL in interfacial polymerization clearly affected the structure of the barrier layer and corresponding NF properties. The smaller ion (BMIC) simultaneously reduced permeation flux and increased salt rejection rate, while the larger ion (OMIC) exhibited an increase in permeation flux but a slight reduction in salt rejection. The demonstrated TFNC membrane exhibited 2 times higher permeation flux compared to that of NF-90 with comparable salt rejection ratio, and comparable permeation flux and salt rejection performance as those of NF-270. (C) 2010 Elsevier B.V. All rights reserved.