2,2-diamino-4,4,6,6-tetrachlorocyclotriphosphazene was synthesized with the reaction of hexachlorocyclotriphospanzene and ammonium hydroxide, and the from the reaction of this with sodium phenoxide, 2,2-diamino-4,4,6,6-tetraphenoxy cyclotriphosphazene was made. These diaminophosphazene derivatives were analyzed with IR, elemental analysis, $^1$H-NMR. Also, the thermal stability of epoxy resins cured with dicyanodiamide, a curing agent in commersial use, and with diaminophosphazene derivatives were examined. As the results of TGA, epoxy resins cured with synthesized curing agents showed better thermal stability than that with dicyanodiamide and were thermally stable up to 270-32$0^{circ}C$. Therefore resins cured with these curing agents are useful for making fire and heat-resistant composites, laminates and adhesives.