1,3,5-Triisopropoxy-1,3,5-tris(4-aminophenoxy)-cyclotriphosphazene-[CTP (I)], 1,3,5-trineopentoxy-1,3,5-tris(4-aminophenoxy)-cyclotriphosphazene [CTP (II)], and 1,1,3,5-tetraneopentoxy-3,5-bis(4-aminophenoxy)-cyclotriphosphazene [CTP (III)] were prepared from hexachlorotricylophosphazene. Thermal decomposition of the crude CTP (I), CTP (II), and CTP (III) was studied by thermogravimetry, differential scanning calorimetry, and thermal volatilization analysis. Solid, gaseous, and high boiling degradation products were collected at different steps of thermal decomposition and identified by using infrared and gas chromatography mass spectrometry. On heating to 600℃, CTP (I) shows three main steps of weight loss, whereas both CTP (II) and CTP (III) show two overlapping steps. The first step of thermal decomposition of CTP (I) is observed at 150-200℃, where elimination of part of the aliphatic substituents and polymerization of the CTP (I) occurs. The opening of tricyclophosphazene rings at 220-370℃ provokes further elimination of aliphatics and ammonia and formation of crosslinked structures. Phosphorus oxynitride structure bonded with carbonized polyaromatics is formed in the third step of thermal decomposition, accompanied by the elimination of aromatics and chain fragments at 400-500℃. In the case of CTP (II) and (III), simultaneous evaporation of virgin CTPs, opening of the phosphazene ring, and elimination of aliphatic substituents with the formation of crosslinked polymeric structures occur at 210-350℃. A phosphorus oxynitride-aromatic carbonized structure similar to that from CTP (I) is formed at 350-600℃. The process is accompanied by the elimination of aromatics and chain fragments.