This study focuses on the surface modification of the thin-film composite polyamide reverse osmosis (RO) membranes by silica (SiO2) nanoparticles. In order to modify RO membranes, the SiO2 nanoparticles were added to amine solution with different concentrations of 0.005 to 0.5 wt.%. The surface structure, hydrophilicity and chemical composition of the membranes were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), contact angle measurements and FT-IR spectroscopy. FT-IR spectroscopy of the synthesized membranes revealed the incorporation of SiO2 nanoparticles on the polyamide active layer. Contact angle measurements showed that the surface hydrophilicity of the membranes increased by increasing SiO2 concentration in the aqueous solution. The SEM images indicated the incorporation of SiO2 nanoparticles in polyamide active layer. The surface roughness of the membranes was increased by increasing the content of nanoparticles in the amine solution. The modified membranes were examined through cross flow permeation tests with NaCl aqueous solution at an operating pressure of 44 bar. The flux of the membranes increased gradually at lower levels of nanoparticles (0.005-0.1 wt.%) and then decreased at 0.5 wt.%. Moreover, the NaCl rejection increased at lower concentration of SiO2 (0.005 and 0.01 wt.%) and then decreased with an increasing content of SiO2. Long-term experiments showed that the modified RO membranes had lower flux decline compared to neat thin film composite RO membrane. (C) 2014 Elsevier B.V. All rights reserved.