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Nitro derivatives of benzotriazoles are safe energetic materials with remarkable thermal stability. In the present study, we report on the kinetics and mechanism of thermal decomposition for 5,7-dinitrobenzotriazole (<b>DBT</b>) and 4-amino-5,7-dinitrobenzotriazole (<b>ADBT</b>). The pressure differential scanning calorimetry was employed to study the decomposition kinetics of <b>DBT</b> experimentally because the measurements under atmospheric pressure are disturbed by competing evaporation. The thermolysis of <b>DBT</b> in the melt is described by a kinetic scheme with two global reactions. The first stage is a strong autocatalytic process that includes the first-order reaction (<i>E</i>_a1^I = 173.9 ± 0.9 kJ mol⁻¹, <i>log</i>(<i>A</i>₁^I/s⁻¹) = 12.82 ± 0.09) and the catalytic reaction of the second order with <i>E</i>_a2^I = 136.5 ± 0.8 kJ mol⁻¹, <i>log</i>(<i>A</i>₂^I/s⁻¹) = 11.04 ± 0.07. The experimental study was complemented by predictive quantum chemical calculations (DLPNO-CCSD(T)). The calculations reveal that the 1H tautomer is the most energetically preferable form for both <b>DBT</b> and <b>ADBT</b>. Theory suggests the same decomposition mechanisms for <b>DBT</b> and <b>ADBT</b>, with the most favorable channels being nitro-nitrite isomerization and C–NO₂ bond cleavage. The former channel has lower activation barriers (267 and 276 kJ mol⁻¹ for <b>DBT</b> and <b>ADBT</b>, respectively) and dominates at lower temperatures. At the same time, due to the higher preexponential factor, the radical bond cleavage, with reaction enthalpies of 298 and 320 kJ mol⁻¹, dominates in the experimental temperature range for both <b>DBT</b> and <b>ADBT</b>. In line with the theoretical predictions of C–NO₂ bond energies, <b>ADBT</b> is more thermally stable than <b>DBT</b>. We also determined a reliable and mutually consistent set of thermochemical values for <b>DBT</b> and <b>ADBT</b> by combining the theoretically calculated (W1-F12 multilevel procedure) gas-phase enthalpies of formation and experimentally measured sublimation enthalpies.