Abstract: A novel reactive flame retardant was synthesized by a twostep procedure from 9,10-dihydro-9-oxa-10-[N, N-bis-(2-hydroxyethylaminomethyl)]-10-phosphaphenanthrene-10-oxide(DAM-DOPO), formaldehyde and diethanolamine, with a strong acid ion exchange resin as a catalyst. The structure of DAM-DOPO was identified by FTIR, 1H-NMR and 31P-NMR. The flame retardant was employed in polyurethane(PUF) and was evaluated using limiting oxygen index, horizontal burning test and CAL 117D. It was found that the melting point of DAM-DOPO was 165~167 ℃. Limited oxygen index of polyurethanes foam(PUF) containing 12 phr DAM-DOPO was 26.5 %. The flame retardancy of PUF passed the CAL TB 117D test and GB 8410—2006.