Nanocomposite membranes comprising two or more layers with different structural properties are used in filtration apparatus. In the present study, polyethersulfone (PES) nanofibrous composite membranes were fabricated by means of electrospinning and the influence of solvent type, temperature and polymer concentration on PES electrospinning process was investigated. To get bead-free nanofibers, electrospinning process parameters were optimized. To fabricate the nanocomposite membranes with varying properties five different flow rates of polymer solutions (0.1, 0.4, 0.7, 1 and 1.3 ml/h) were used. Solvent vapor treatment was carried out to enhance the mechanical properties of the nanocomposite membranes by increasing the fiber adhesion. Morphology of the membranes was studied using scanning electron microscope, and mechanical properties were evaluated by tensile test. Pore size of the membrane was assessed by bubble point method. Retention test was conducted using nanoparticle suspensions containing equally sized particles and the water flux was measured through dead-end filtration system. Finally, fabricated membranes were used for filtering out bacteria and fungus from culture media. Results show that the fiber diameter, fiber adhesion and also membrane thickness have significant impact on potential membrane retention, water flux and bacterial removal.