A　series　of　novel　magnetic　nanoparticles　(MNPs)　with　various　sizes　for　forward　osmosis　(FO)　applications　were　synthesized　via　a　one-pot　reaction　under　mild　conditions.　The　newly　developed　MNPs　are　coated　with　three　different　hydroacids　(citric　acid,　oxalic　acid　and　EDTA)　carrying　abundant　carboxylic　groups　which　could　make　the　hydroacid-MNPs　highly　dispersible　and　ionizable　in　water.　These　features　enable　the　aqueous　solutions　of　hydroacid-MNPs　to　produce　osmotic　pressures　and　FO　water　fluxes　comparable　to　the　traditional　draw　solutions　yet　with　a　negligible　reverse　flux.　The　experimental　results　indicate　that　better　FO　performance　was　achieved　when　the　hydroacid-MNPs　with　smaller　sizes　were　applied　to　the　FO　process.　With　the　model　seawater　of　3.5 wt%　NaCl　as　the　feed　solution,　the　citric　acid　coated　MNPs　produced　a　water　flux　of　8.5　LMH,　which　is　much　higher　than　those　reported　for　MNPs　draw　solutes　applied　in　FO　for　seawater　desalination.　Additionally,　the　hydroacid-MNPs　were　readily　regenerated　from　their　diluted　solutions　after　FO　via　an　integrated　system　including　both　magnetic　and　membrane　separations.　This　study　significantly　extends　the　potential　applicability　of　FO　and　provides　an　economical　approach　for　efficient　seawater　desalination　via　hydroacid-MNPs　promoted　FO　processes.　©　2016　Elsevier　B.V.