The latent heat of vaporization of water in foodstuffs is an important factor for the design of drying equipments. The thermal properties can be calculated by equations that are derived directly from isotherm equations by the Clausius-Clapeyron thermodynamic theory. The sorption isosteric heat equation can be expressed as a function of temperature and moisture content. The sorption isosteric heat computed from the water activity (A,) sorption isosteric model developed in this study showed good agreements with the values calculated by the Clausius-Clapeyron equation or from calorimetric method. As the A, model had the better fitting performance, the sorption isosteric beat values calculated from the water activity sorption isosteric model were more close to the sorption isosteric heat values obtained from other methods. (c) 2005 Elsevier Ltd. All rights reserved.