Thermal stabilities and thermal decomposition mechanisms of amino-functionalized ionic liquid (IL) 1-aminoethyl-3-methylimidazolium bromide ([C2NH2MIM][Br]) and hydroxyl-functionalized IL 1-hydropropyl-3-methylimidazolium chloride ([C3OHMIM][Cl]) were investigated by thermogravimetric analysis (TGA), TG-mass spectroscopy (TG-MS), density functional theory (DFT), and nuclear magnetic resonance (NMR) spectrum. Results show that the [C2NH2MIM][Br] and [C3OHMIM][Cl] are stable up to 200 degrees C and 220 degrees C, respectively. Also, DFT calculation indicates that the thermal decomposition mechanisms of [C2NH2MIM][Br] and [C3OHMIM][Cl] are complicated, while bimolecular nucleophilic substitution (SN2) is the main reaction mechanism. TG-MS and NMR spectra further prove the mechanisms. (C) 2014 Elsevier B.V. All rights reserved.