Nitro-5-guanidino-1,2,4-oxadiazole (NOG) was obtained by oxidation of diaminoglycoluril (AG) with in situ generated dimethyldioxirane (DMDO). The particle morphological appearance of NOG prepared with the quick precipitation method was studied by scanning electron microscopy (SEM). The thermal behavior of NOG was studied by differential scanning calorimetry (DSC) and differential thermal/thermo-gravimetric analyzer (TG-DTA). The apparent activation energy (E) and pre-exponential factor (A) of the exothermic decomposition reaction,the peak temperature (TP0) of heating rate β→0, and activation entropy (ΔS≠), activation enthalpy (ΔH≠),activation Gibbs free energy (ΔG≠) at TP0 of the reaction and the critical temperature of thermal explosion (T_b) were calculated. The results show that NOG has better heat-resistance ability. The decomposition temperature of NOG is 290 ℃. The critical temperature of thermal explosion (T_b) is 291.56 ℃, ΔS≠ is 232.35 J·k-1·mol-1, ΔH≠ and ΔG≠ is 267.36 kJ·mol-1 and 138.42 kJ·mol-1, respectively. 