Currently, polyamide reverse osmosis membranes are highly effective for desalination, industrial process water, and home drinking water. However, they have poor resistance to strong oxidants especially chlorine due to chain cleavage of aromatic polyamide. In general, aromatic polyamide RO membranes are essentially random copolymers consisting of the linear and crosslinked structures. The amide ring is sensitive to attack by chlorine because it is an electron-rich region. Therefore, the activated carbon or sulfite addition processes are essential to remove the chlorine in the separation processes. Many research groups have studied to improve the chlorine-resistance RO membrane having hydrophilic groups (-SO3H and -COOH) or nitro groups (-NO2) such as electron acceptors. In this study, thin film composite polyamide RO membranes were prepared by interfacial polymerization method including cross-linking agents having hydroxyl groups to improve the chlorine-resistance. The chlorine-resistance of polyamide RO membrane was influenced by the thermal cross-linking conditions (temperature and time) and cross-linking density of polyamide membranes. (C) 2009 Elsevier B.V. All rights reserved.