Cross-linked　PS-DVB/Fe3O4　microspheres　(PFM-3)　have　been　successfully　synthesized　by　a　new　magnetic　colloid　swelling　polymerization　method　and　further　functioned　by　alternatively　using　methylamine　and　1,4-butanediol　diglycidyl　as　monomers　to　build　a　branching　polymer　with　quaternary　ammonium　groups.　The　characterization　of　PFM　has　been　performed　by　XRD,　FT-IR,　SEM,　TEM　and　BET　surface　area　analyses.　The　results　showed　that　PFM-3　possessed　a　high　ion　adsorption　capacity　(149.25　mg　g-1)　and　could　adsorb　nitrate　ions　from　water　efficiently.　The　material　also　showed　excellent　reusability　(after　washing　with　sodium　chloride,　the　absorption　capacity　was　little　reduced).　More　importantly,　the　magnetic　microspheres　could　be　removed　from　waste　water　easily　via　introducing　an　external　magnetic　field,　which　made　the　discoveries　in　this　study　provide　an　effective　and　environmentally　friendly　approach　for　fast　removal　of　nitrate　from　waste　water.　©　The　Royal　Society　of　Chemistry.