Abstract Thermal decomposition of octahydro-2,5-bis(nitroimino)imidazo[4,5- d ]imidazole was studied by means of thermogravimetry (TG) and differential thermal analysis (DTA) simultaneously under nitrogen atmosphere. The structure of the compound was also estimated by a B3LYP method based on the 6-31G(d,p) basis set to obtain a stable geometric configuration and the corresponding Wiberg bond order. The results indicate that the compound shows good thermal stability with exothermic decomposition peak at 335°C on DTA, the geometric structure of the compound presents a little contorted configuration and the C(3)—N(22) bond order is weaker than the other N—N or C—N bonds.