New 1,3-propanediaminocyclotriphosphazene derivatives (7–17) were synthesized from the reactions of spiro-1,3-propanediaminocyclotriphosphazene, N 3 P 3 Cl 4 [NH(CH 2 ) 3 NH] (1) with the cyclopropanemethylamine (2), cyclohexylamine (3), pyrrolidine (4) cyclohexanol (5), cyclopropylmethanol (6). The structures of the novel compounds (7–17) were characterized by elemental analysis, mass spectrometry, 1 H and 31 P NMR spectroscopy. The molecular structures of 8, 12 and 13 were determined by X-ray crystallography. The structures of all these three compounds are in the monoclinic crystal system; compounds 8 and 12 have the P21/c space group while compound 13 has the P21/n space group. The ring conformation of the cyclotriphosphazene and other external rings were investigated based on the X-ray crystal structures.