Hexakis-(4-aminophenoxy)-cyclotriphosphazene (PN-NH2) was synthesized through nucleophilic substitution of the chloride atoms of hexachlorocyclotriphosphazene (HCCP) and reduction of the nitro group, and its chemical structure was characterized. As a curing agents for commercial epoxy resin Diglycidyl ether of bisphenol-A (DGEBA) PN-NH2 was compared with conventional curing agents 4,4-diaminodiphenylsulfone(DDS) and 4,4-diaminodiphenylmethane (DDM). The thermal properties and thermal degradation behaviors of these thermosetted resins were investigated by using thermogravimetric analysis (TGA). TGA studies demonstrated that the thermal properties of the PN-NH2-containing cured epoxy resin were higher than those of others. The phosphorus-nitrogen containing curing agent can result in a great improvement of the flame retardance for their thermosetted epoxy resins.