The　increase　of　agricultural　related　activities　and　the　lack　of　effective　waste　control　has　led　to　an　increase　of　organic　nitrogen　in　water.　The　development　of　coagulants　to　effectively　remove　dissolved　organic　nitrogen　(DON)　is　a　high　priority　in　the　water　treatment　industry.　We　developed　a　polymeric　zinc-iron-phosphate　(Zn.　Fe.　P)　coagulant　and　investigated　its　coagulation　effect　on　DON　removal.　Optimum　coagulant　for　coagulation　for　DON　and　TDN　removals　was　characterized　by　the　dense　convex-concave　packing　structure　differing　from　other　zinc-based　coagulant,　polycrystalline　structure　and　high　content　colloidal　species,　which　could　account　up　to　87%　of　the　total　colloidal　species.　Coagulation　experiments　showed　the　DON　removal　rate　to　vary　greatly　depending　on　principal　components　and　their　interaction　with　metals,　phosphate　and　hydroxyl.　DON　removal　efficiency　increased　with　the　increase　of　colloidal　species.　The　coagulation　was　also　dependent　on　coagulant　dosage　and　water　quality　parameters:　Coagulation　efficiency　increased　with　coagulant　dosage　in　the　investigated　range　of　1-16　mg/l,　and　a　pH　of　6　was　found　to　be　superior　for　the　coagulation.　DON　removal　efficiency　was　also　higher　than　and　linearly　correlated　with　total　dissolved　nitrogen　(TDN)　removal,　which　implies　that　an　effective　coagulation　for　TDN　is　also　effective　for　DON.　The　findings　in　this　study　indicate　that　coagulation　of　DON　is　largely　influenced　by　coagulant　composition　and　species.　We　also　found　the　removal　of　DON　by　our　newly　developed　polymeric　Zn.　Fe.　P　coagulant　to　be　effective.　©　2016　Elsevier　Ltd.