In this work, a new strategy for fabrication of high flux thin film nanofibrous composite (TFNC) ultrafiltration membrane containing a hydrophilic barrier layer and a nanofibrous substrate was developed. Firstly, the double-layer nanofibrous mat containing very thin hydrophilic nanofiber top layer and nanofibrous supporting layer was manufactured via electrospinning technique. Then the hydrophilic nanofibrous top layer was remelted by suitable solvent vapor exposure and chemical crosslink in the crosslinking bath to form a barrier film on the supporting layer. Here, poly(vinyl alcohol) (PVA)/polyacrylonitrile (PAN) nanofibrous composite membranes were prepared by electrospinning of a very thin PVA nanofibrous layer with thickness of several micrometers on the electrospun PAN nanofibrous substrate, followed by remelting PVA nanofibrous layer to form a barrier PVA film by water vapor treatment and chemical crosslinking in glutaraldehyde water/acetone solution. The depositing time during PVA electrospinning and the water content of the crosslinking solution were utilized to control the thickness and the swelling degree of the PVA barrier layer. In this method, the shortcoming of easy penetration of the coating solution into the porous substrate in typical fabrication of surface coated anti-fouling composite membranes can be overcome, and the thickness of the barrier layer can be easily controlled by the depositing time of the PVA electrospinning. Filtration performances of the PVA/PAN composite membranes were evaluated by the oil/water emulsions separation system. The highest permeate flux of 2101/m(2)h was achieved with the rejection of 99.5% for the composite membrane under the operating pressure of 0.3 MPa. It is believed that the strategy for fabricating TFNC membranes described here can be extended easily to fabricate nanofibrous composite membranes from many other polymeric materials simply by choosing the suitable solvent vapor treatment. (C) 2010 Elsevier B.V. All rights reserved.