Four hydroxyl-functionalized ionic liquids, 1-(6-hydroxyhexyl)-3- alkylimidazolium chlorides 6OHimCnCl; (n = 0, 1, 2, 4), have been synthesized from the appropriate imidazole precursors and characterized by IR and NMR spectroscopies and elemental analysis. Densities, dynamic viscosities, refractive indices, and surface tensions have been measured for each liquid as a function of temperature at atmospheric pressure and fitted using simple empirical correlation functions. Consistent with related imidazolium-based ionic liquids, an increase in the carbon side-chain length of the imidazolium cation was found to decrease the density and surface tension but increase the viscosity and refractive index. Cytotoxicities of the present liquids were found to decrease with increasing carbon side chain length and were broadly similar to those of other ionic liquids. © 2011 American Chemical Society.