The thermophysical properties of hydroxyl ammonium ionic liquids: density rho, T = (293.15 to 363.15) K; dynamic viscosity eta, 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 alpha, 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). (C) 2008 Elsevier Ltd. All rights reserved.