The thermophysical properties of hydroxyl ammonium ionic liquids: density ρ , T = (293.15 to 363.15) K; dynamic viscosity η , T = (298.2 to 348.2) K; and refractive indices n D , T = (293.15 to 333.15) K have been measured. The coefficients of thermal expansion α , values were calculated from the experimental density results using an empirical correlation for T = (293.15 to 363.15) K. The variation of volume expansion of ionic liquids studied was found to be independent of temperature within the range covered in the present work. The thermal decomposition temperature ‘ T d ’ for all the six hydroxyl ammonium ionic liquids is also investigated using thermogravimetric analyzer (TGA).