• [C 2 mmim]NO 3 could cause an explosion or other hazard problems. • Various analysis instruments were applied to analyze the thermal stability. • Thermokinetic parameters were calculated by two isoconversional methods. • A homemade combustion test device was used to assess the flammability. • The possible combustion process of [C 2 mmim]NO 3 was determined. 1-Ethyl-2, 3-dimethylimidazolium nitrate [C 2 mmim][NO 3 ] is a typical solvent for industrial applications. Under inappropriate temperatures, [C 2 mmim][NO 3 ] may present a flammability hazard due to thermal decomposition. This study investigated the thermal stability and flammability of [C 2 mmim][NO 3 ] via simultaneous thermogravimetric analyzer, homemade combustion test device (CTD) with high speed camera, and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR). The thermal decomposition of [C 2 mmim][NO 3 ] was divided into two parts based upon the dynamic experiments, and the maximum operating temperature was determined to comprehensively estimate the thermal stability of [C 2 mmim][NO 3 ]. CTD experiments indicated that [C 2 mmim][NO 3 ] could produce intense combustion when heated. Further TG-FTIR experiments confirmed that [C 2 mmim][NO 3 ] decomposed to produce a large number of flammable gases, such as ethylene, which might be the reason that [C 2 mmim][NO 3 ] has prominent flammability. [ABSTRACT FROM AUTHOR]