In this work, composite polyamide reverse osmosis (RO) membranes were synthesized by interfacial polymerization of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers over a polyethersulfone (PES) support layer. Four PES support membranes were prepared by a non-solvent-induced phase separation method using hydrophilic additives such as polyvinylpyrrolidone (PVP) and poly (ethylene glycol) (PEG). For this purpose, the influence of lag time on the properties and performance of the fabricated thin film composite (TFC) membranes was investigated. The separation performance of TFC membranes was evaluated by a cross flow flat sheet RD membrane unit. Besides, surface properties and surface morphology as well as hydrophilicity of PES support membranes and TFC membranes were examined by AFM, FE-SEM, ATR-FTIR and contact angle (CA) analyses, respectively. The results showed that adding hydrophilic agents in the PES supports improves water permeability, surface properties and pore size. The effect of lag time on the separation performance of the fabricated TFC membranes was more significant than the effect of pore size and hydrophilicity of support layer. Generally, the results confirmed that lag time plays an important role in the synthesis process and affects the separation and surface properties of the polyamide TFC membranes. (C) 2011 Elsevier B.V. All rights reserved.