Abstract The thermal decomposition behaviour of poly-1-vinyl-5-aminotetrazole (P-1VAT) was studied by high-resolution thermogravimetry, differential scanning calorimetry and thermal volatilisation analysis. P-1VAT decomposes in two steps. Two parallel processes of the tetrazole ring splitting in the amino-tetrazole pendant group, which evolve either nitrogen or hydrogen azide, are considered to be the first step. The partial volatilisation of the melamine, formed in the first step, and polymer chain fragments are observed in the second step. On thermal decomposition under nitrogen, P-1VAT produces a 28% residue which is thermostable at 600°C and which consists of a cross-linked polymer network, melem and melon.