The dextran coated Fe₃O₄ magnetic nanoparticles (MNPs) have been successfully synthesized and used for brackish water desalination for the first time. The dextran coated Fe₃O₄ MNPs well meets the stringent criteria for draw solutes of forward osmosis (FO) process via technologically integrating the good solubility of dextran and strong magnetism of Fe₃O₄ nanoparticles. Our experimental results demonstrated that the dextran coated Fe₃O₄ MNPs are not only able to produce high osmotic pressure to draw clean water across FO membranes from brackish water, but also can be easily recovered from the diluted draw solution by an external magnet. Based on our currently conducted works, it is believed that the dextran coated Fe₃O₄ MNPs can be an ideal draw solute for brackish water desalination by using FO process in an environmental-friendly and energy-saving manner.