Aminopropyl-functionalized MCM-41 (NH2-MCM-41) was synthesized by the one-pot hydrothermal method using tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES) as silica sources, cetyltrimethylammonium bromide as template, ethanol as a cosolvent, and sodium hydroxide as the alkali source. The synthesized nanoparticles were noticeably monodisperse with standard deviation of under 10% for the mean particle size. The specific surface area, pore size, pore volume and amino group density of the NH2-MCM-41 varied with the content of APTES in the initial solution. The NH2-MCM-41-polyamide thin film nanocomposite reverse osmosis (TFN RO) membranes were obtained by interfacial polymerization of trimesoyl chloride (TMC) and m-phenylene-diamine (MPD). The hydrophilicity of the TFN RO membranes was improved by the incorporation of NH2-MCM-41 nanoparticles. The water flux of 54 L m−2 h−1 at 1.6 MPa for NH2-MCM-41-polyamide TFN RO membrane was nearly 2.8 times that of the pure polyamide thin film composite (TFC) RO membrane and the solute rejection was 96.5% with a 0.1% w/v NH2-MCM-41 loading.