Thermal diffusivity of eutectic formed in aqueous alkali chloride solutions (NaCl, KCl, RbCl and CsCl) was determined by temperature wave analysis (TWA) during the freezing-thawing process of aqueous alkali chloride solution. An obvious change of thermal diffusivity in freezing-thawing processes of eutectic was observed with the super-cooling phenomena for each alkali chloride solute. The rate of thermal diffusivity decrease during the eutectic melting in comparison to the total decrease from the solid to the liquid state was observed larger than that of the heat of fusion measured by DSC, especially in the dilute concentration. It was confirmed that thermal diffusivity was sensitively influenced by the highly structure of the coexistence of eutectic crystallization and ice. (c) 2004 Elsevier B.V. All rights reserved.