Thermal decomposition onset temperatures have been measured for a total of 24 methylimidazolium, triethanolammonium, and pyridinium type sulfonic acid groups functionalized Brönsted acidic ionic liquids with Cl-, Br-, SO42-, PO43-, BF4-, CH3CO2-, and CH3SO3- anions, using thermogravimetric analysis. Thermal stabilities of these sulfonic acid group functionalized ionic liquids decreases in the order, methylimidazolium > triethanolammonium > pyridinium. The methylimidazolium, pyridinium, and triethanolammonium ionic liquids investigated showed decomposition onset temperatures (air) in the 213-353, 167-240, and 230-307 °C ranges, respectively. Additionally, the decomposition temperatures of these ionic liquids are highly dependent on the nature of the anion. © 2010 Akadémiai Kiadó, Budapest, Hungary.