A facile approach was developed to simultaneously functionalize and reduce graphene oxide (GO) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-phosphonamidate. To achieve stable dispersion and effective stress transfer, graphene was functionalized by polyethyleneimine (PEI). To improve the fire resistance of bare graphene, DOPO was grafted on the surface of PEI-reduced graphene oxide (PEI-rGO) to obtain the grafting of DOPO-phosphonamidate on the graphene. A morphological study indicated that, due to the good interfacial interaction between the functionalized graphene and epoxy (EP), functionalized reduced graphene oxide (f-rGO) was well-dispersed in the host polymer. Incorporation of 3.0 wt% f-rGO led to the increased char yields of the EP. Moreover, the storage modulus and glass transition temperature were improved, respectively. The evaluation of combustion behavior demonstrated that the peak heat release rate and total heat release of f-rGO/EP were reduced by 31% and 34.3%, respectively, compared to those of neat EP. This dramatically reduced fire hazards were mainly attributed to the synergistic effect of f-RGO. On one hand, DOPO-phosphonamidate on the surface of GO promoted flame inhibition in the gas phase while protecting the rGO against fire. On the other hand, the adsorption and barrier effect of rGO inhibited the heat and gas release, respectively, promoting the formation of graphitized carbons. (C) 2018 Elsevier Inc. All rights reserved.