Nanocomposite membranes containing polyethersulfone (PES) and organically modified montmorillonite (OMMT) were prepared by a combination of solution dispersion and wet-phase inversion methods and accordingly, the effect of OMMT addition to the properties and performance of fabricated nanofiltration membranes was investigated. The membranes were characterized by contact angle measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), mechanical strength evaluation, thermogravimetric analysis (TGA), and zeta potential. The performance of the membranes was elucidated by the removal of pesticides (nitrophenols (NPs)) in neutral and acidic pHs. The hydrophilicity of the membranes was strongly enhanced by increasing the OMMT concentration. The SEM and AFM images showed that addition of OMMT to the casting solution resulted in nano-structure membranes with a thinner skin layer and a smaller surface pore size. XRD patterns revealed the formation of intercalated and exfoliated layers of mineral clays in the PES matrix which was also confirmed by TEM images. The addition of OMMT improved the mechanical properties and thermal stability of the membranes. Moreover, the pure water flux, permeation and, rejection of NPs were significantly improved. The performance of fabricated NF membranes in removal of NPs varied depending on the solute and membrane properties as well as solution condition. Finally, a comparison between fabricated membranes and a commercial NF membrane (NF45, Dow Filmtec) proved that the OMMT addition is a convenient procedure for producing nanocomposite membranes with superior characterization and performance. (C) 2011 Elsevier B.V. All rights reserved.