The thermophysical properties of hydroxyl ammonium ionic liquids: density �, T = (293.15 to 363.15) K; dynamic viscosity η, T = (298.2 to 348.2) K; and refractive indices nD, 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 'Td' for all the six hydroxyl ammonium ionic liquids is also investigated using thermogravimetric analyzer (TGA). © 2008 Elsevier Ltd. All rights reserved.