Caged bicyclic phosphate (CBP) and its dimelamine salt (PDS) were synthesized and added to epoxy resins to obtain the flame retarded epoxy resin composites. The flammability of the composites was characterized by the limiting oxygen index (LOI) and cone calorimeter tests. The LOI values of flame retarded composites increase consistently with the increase of flame retardant amounts, and they are almost the same when the loading of CBP is the same as that of PDS,although the phosphorus content of PDS is much lower than that of CBP. The total heat release increases in the order of CBP30/ER ＜ PDS30/ER ＜ PDS15/ER ＜ CBP15/ER, whereas that of specific extinction area is CBP15/ER ＞ CBP30/ER ＞ PDS30/ER ≌ PDS15/ER. PDS exhibits more effective inhibition of oxidation of combustible gases. In the tests of thermogravimetric analyses (TG) and Fourier transform infrared spectroscopy (FT-IR), it is found that the degradation of the composites is influenced greatly by the addition of flame retardants. By scanning electron microscopy (SEM), a thick and tight char-layer is observed for PDS30/ER, resulting from the interaction of nitrogen species with phosphorus species.Therefore, the combination of CBP with melamine in the flame retarded system can improve the flame retardancy greatly.