This study investigates how surface modification of RO membranes enhances resistance to fouling. The standard mechanisms of membrane fouling are extended to identify RO pretreatment processes. The degree of fouling resistance of modified RO membranes are studied with respect to the modified fouling index (MFI). According to the definition of the MFI, the higher the MFI value of an RO membrane indicate the greater the fouling resistance. A polysiloxane system consisting of 3-glycidoxypropyltrimethoxysilane (GPPTMS) modified on a PA surface displays a complex structure. The fouling resistance of the GPPTMS-modified RO membrane was increased by using a hydrophilic epoxy compound, which forms hydrolyzed functional groups. The flux decline index (m) and the MFI decreased for GPPTMS concentrations less than 1.0 wt%. These results prove that fouling of GPPTMS-modified RO membranes would be reduced when the concentration of GPPTMS was over 1.5 wt%. The values of m and MFI for RO membrane are much higher than those for GPPTMS-modified RO membranes because more foulants are brought to the membrane surface. (C) 2016 Elsevier B.V. All rights reserved.