One of the big challenges for forward osmosis (FO) practical application is the lack of high performance FO membranes. In this research, we successfully fabricated a novel thin film nanocomposite (TFN) FO membrane consisting of a polyetherimide (PEI) nanofibrous substrate reinforced by functionalized multi-walled carbon nanotubes (f-CNTs) and an ultrathin polyamide rejection layer. In addition to the superior inter-connected porous structure of nanofibrous substrate, the well-distributed f-CNTs in the nanofibers increased the substrate porosity by 18% and reduced membrane's structural parameter (S value) by 30%, and significantly improved the substrate tensile modulus by 53%. The high mechanical strength provided by the embedded f-CNTs enabled us to further increase the substrate pore size and porosity in order to mitigate the internal concentration polarization (ICP). This was demonstrated by the high performance TFN-2 FO membrane with a structural parameter of 310 pm. Its water flux at 1.0 M NaCl draw solution (DS) was as high as 61 and 33 L/m(2) h in the active layer facing draw solution (AL-DS) and active layer facing feed water (AL-FW) orientations, respectively, indicating the success of the design strategy, i.e., improved membrane mechanical strength enables a further improvement of the membrane structure to mitigate the ICP. (C) 2015 Elsevier B.V. All rights reserved.