The forward osmosis (FO) membrane separation process is one of the emerging membrane technologies that can meet the increasing global demand for clean water. We synthesize the Fe3O4/SiO2 core/shell particles functionalized with sodium polyacrylate (PNaAA) as a draw solute, which generates the driving force to transport water through an FO membrane in this process. The Fe3O4 core enables the recovery and dispersion of the particles using a magnetic field, while the grafted PNaAA provides the high osmotic pressure required to transport water. Preparing an SiO2 shell over the Fe3O4 core of the particles enables the chemical immobilization of the PNaAA on the particle surface and increases their stability as a draw solute. Here, Fe3O4 core particles with a controlled size of the submicron-meter order are prepared by a solvothermal method, followed by the formation of the SiO2 shell. Subsequently, the Fe3O4/SiO2 core/shell particles are modified with PNaAA using surface-initiated atom transfer radical polymerization (SI-ATRP). The effects of the amount of grafted PNaAA and the particle size on the performance as a draw solute are investigated by conducting osmolality measurements and recovery tests. The synthesized particles are able to maintain a stable dispersion even after ten cycles of assembling/dispersing operations. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.