Contact angle measurement is conducted to determine surface hydrophilicity of RO membrane with the intention of predicting membrane performance or fouling potential. Most researchers of membrane technology have used contact angles without considering effective factors for contact angle measurement such as measurement time, drop volume and membrane sample preparation. In fact, significantly different contact angles are reported even on the same RO membrane. In this study, contact angles were measured by the sessile drop method and captive bubble method and were compared with various conditions such as measurement time, drop volume, membrane sample preparation and liquid type in the commercialized RO membranes. As a result. sessile drop method showed unreliable contact angles, which varied dramatically with the preparation conditions. On the other hand, the captive bubble method, which represents conditions closer to the real RO membrane process, showed reproducible contact angles. For the different commercially available RO membranes, similar hydrophilicity was observed. Overall, the captive bubble method appears to be a more adequate method for measuring contact angle of RO membranes. (C) 2012 Elsevier B.V. All rights reserved.