1,3-Dimethylimidazolium nitrate ([Mmim]NO3), an ionic liquid, is a versatile and novel solvent for the petrochemical industry. Nevertheless, under high temperature conditions or thermal upset scenarios, [Mmim]NO3 can be decomposed in a manner that produces an explosion or other serious safety problems. The aim of this research was to investigate the thermal stability of [Mmim]NO3 by simultaneous thermogravimetric analyzer and high pressure differential scanning calorimetry. Isothermal experiments indicated that [Mmim]NO3 would be decomposed at a temperature substantially lower than the onset temperature. A pseudo-zero-order rate expression was applied to characterize the thermal decomposition kinetics of [Mmim]NO3, and related thermokinetic parameters were further obtained. Moreover, the temperature at which the thermal decomposition of ILs reached 10.0% for a given time of 10.0 h (T-0.1/10h) was defined to assess the long-term thermal stability, which can be used as the maximum operating temperature of [Mmim]NO3. The results of this study may provide relevant processes for safer control based on the thermal hazard assessment of [Mmim]NO3. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.