Most water-based filtration applications of electrospun nanofibrous membranes require the substrate to possess suitable strength, wettability and permeability, where the size, inter-fiber adhesion and hydrophilicity of electrospun nanofiber must be carefully controlled in order to meet these criteria. In this study, we demonstrate the fabrication of high quality polyethersulfone (PES) nanofibrous membranes that are particularly useful for water purification. Two treatments were illustrated that can significantly improve the mechanical property and hydrophilicity of the PES membrane without compromising its porosity and water permeance. The first treatment involves the use of mixed solvents (DMF/NMP), containing a high vapor pressure component (NMP), where the mechanical properties (e.g. modulus and strength) of the membrane are improved by solvent-induced fusion of inter-fiber junction points. The second method involves the short time oxidation treatment with a strong oxidant (ammonium persulfate), where the hydrophilicity of the membrane is greatly increased. (C) 2009 Elsevier Ltd. All rights reserved.