In this research, mixtures of Cu(NO3)(2) and AgBF4 salts were used in preparation of poly(ethersulfone) (PES)/poly(ethylene oxide) (PEO) composite facilitated transport membranes. Reduction of carrier agent is known as the main challenge for this type of membranes. The effect of salt blending on the reduction behavior of silver carrier sites was analyzed through permeation and structural properties of composite membranes. Based on UV-Visible, mixed and ideal permeation experiments, the existence of copper divalent cations beside silver monovalent cations will result in delay in reduction time of silver cations. Therefore, the membrane selectivity is retained at higher values. However, starting selectivity of membranes containing silver salt ions (case 2) with concentration above threshold level is higher than other membranes containing both salts (case 1). TEM analysis proved that size and quantity of silver nanoparticles in the membranes of case 1 are less than membranes of case 2. Applying copper salt increased the potential of ions aggregated distribution in membranes structure according to FTIR-ATR analysis. Aggregation is one of the reasons for less initial separation potency in comparison with membranes without copper salt. Incorporation of cooper salt enhanced the surface roughness and mechanical strength of initial membranes containing silver salt alone. (C) 2012 Elsevier B.V. All rights reserved.