Abstract.A novel kind of thin-film nanofibrous composite (TFNC) nanofiltration (NF) membranes consisting of a polyamide (PA) barrier layer were successfully fabricated by interfacial polymerization (IFP) based on electrospun double-layer nanofibrous substrates, which have an ultrathin poly (acrylonitrile-co-acrylic acid) (PAN-AA) nanofibrous layer as top layer and a thicker polyacrylonitrile (PAN) nanofiber layer as bottom porous support layer. Immersing PAN/PAN-AA nanofibrous substrates into 1-ethyl-(3-3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) aqueous solution and piperazine (PIP) aqueous solution (0.20 wt%) sequentially for a period of time, the carboxyl groups on PAN-AA nanofibers were activated by carbodiimide and then reacted with the amide groups. The as prepared composite membrane has an integrated structure with high rejection rate (98.0%); high permeate flux (40.4 L/m 2 h) for MgSO 4 aqueous solution (2 g/L). IntroductionTFNC membranes have been proven to be an effective media for nanofiltration (NF) and reverse osmosis (RO), which structure with a thin and dense functional barrier layer supported on a reinforced porous substrate [1][2][3][4]. The ultra-thin dense barrier layer is usually obtained through interfacial polymerization (IFP), by which the filtration performance of TFNC membranes is mainly determined. The conventional reinforced porous matrix is a less porous dense asymmetric membrane made by phase inversion methods. In recent decades, electrospun nanofibrous membranes have been used as supporting materials in composite membranes due to its high porosity (up to over 80%), interconnectivity, micro scale interstitial space, and a large surface-to-volume ratio [5][6][7]. But it is difficult to fabricate a structure-integrated nanofibrous composite NF membrane because the pore size of electrospun nanofibrous support is relatively large (submicron level) to support strugglingly the ultrathin barrier layer (~ 100 nm thickness) prepared IFP method [8].In this study, a new kind of TFNC membrane was fabricated by introducing a PAN-AA intermediate layer between PA barrier layer and PAN nanofibrous substrate. Carboxyl groups on PAN-AA nanofibers were activated by EDC/NHS and reacted with secondary amine group on PIP,