This study systematically investigated the structure and performance of integrally asymmetric and thin film composite (TEC) FO membranes to gain a better understanding of the FO transport mechanism, and to suggest appropriate characteristics of FO membranes. The effect of structure parameters (S) on the performance of the membranes was also examined. Under various operating conditions, TFC membranes yielded superior J(w), than integrally asymmetric CIA-based membranes, especially, with larger J(w) leading to higher solute resistance at alkaline feed and draw solutions. However, the integrally asymmetric membranes possessed smoother surfaces, resulting in lower fouling propensity than the polyamide TFC membranes. Besides the structure, chemical composition of the skin layer also affected the performance. TFC membranes from Toray Chemical Korea (TCK) showed lower oxygen atomic content on the active layer (AL), higher negatively charged AL and higher fouling propensity compared to the TFC HTI membrane. The TCK membrane with a woven substrate served as a promising membrane, with 2.25 times higher J(w) and 1.48 times less J(s)/J(w) than the TFC HTI membrane. This study showed that a preparation of FO membranes with both enhanced antifouling resistance and TCK membrane-like open and thin structure are required to develop FO membranes with desirable characteristics. (C) 2015 Elsevier B.V. All rights reserved.