To understand the effects of the hydrophilicity of the support layer on the formation of the active layer and the performance of composite membranes, a support layer was prepared from a polysulfone (PSf) blend with a hydrophilic copolymer, and then its top surface was overcoated with an active layer fabricated by an interfacial reaction of m-phenylenediamine (MPDA) with trimesoyl chloride. The time required for impregnating the support layer with an aqueous solution containing MPDA was gradually decreased by increases in the hydrophilicity of the support layer. The required soaking time was greater than 9 min for the formation of the defect-free active layer when the support layer prepared from PSI was used, whereas it could be reduced about 1 min by the use of the hydrophilic support layer. Furthermore, composite membranes prepared with the PSf/hydrophilic copolymer blend as the support layer always exhibited higher salt rejection and water permeability than those prepared with PSf as the support layer. (C) 2007 Wiley Periodicals, Inc.