Recently forward osmosis (FO) has attracted growing attention on many potential applications such as wastewater treatment, desalination and power generation. FO performance is primarily limited by the presence of internal concentration polarization (ICP), which significantly reduces the permeate flux. This study explores the relationship between the physicochemical properties of the solution against the membrane support layer and ICP by incorporating constrictivity. Four solutions with different diffusivities, ion/molecule sizes and viscosities were systematically investigated using a bench-scale FO system. It is found that ICP in the support layer is strongly dependent on the physicochemical properties of the solution facing the support layer. When the solution against the membrane support layer has a lower aqueous diffusivity but larger ion/molecule size and higher viscosity, The ICP phenomenon will be more severe, resulting in lower water flux. The identical diffusion direction of the feed solute and the water flux may reduce the effective diffusivity of the solute in the support layer when the feed solution facing the membrane support layer, resulting in high concentrative ICP. These findings have significant implications for the development of new draw solutes, the pretreatment of the feed solution and the selection of the membrane orientation. (C) 2011 Elsevier B.V. All rights reserved.