The laser-induced thermal grating technique (LTG) has proved to be suitable for the accurate measurement of the thermal diffusivity of pure liquids, liquid mixtures and aqueous solutions of inorganic substances in a wide range of temperatures. Compared with conventional measurement methods, this optical technique has the advantage that no sensors need to be inserted in the sample, especially when measurements have to be made on electrically conducting and corrosive liquids such as aqueous solutions of salts. Due to the tiny temperature rise in the sample during measurements, the short measuring time, and the very small sample volume, the influence of free convection in the sample on the measurement is negligible. In this paper, the laser-induced thermal grating technique (LTG) and the experimental facility are described. Experimental results for aqueous solutions of inorganic salts, e.g. sodium chloride and magnesium chloride etc., are presented which are of importance for understanding a variety of chemical processes in engineering, including desalination processes and corrosion in heat exchangers.