Experimental data on desorption isotherms of three types of clay at different temperatures (40, 50 and 60degreesC) were determined using a static method. The results were fitted by the famous Guggenheim-Anderson-deBoer (GAB) model. The thermodynamic functions, differential heat of sorption, net integral enthalpy and entropy, were evaluated at several moisture contents. Heat of sorption decreased with the moisture content and the trend became asymptotic as the moisture content of 0.01 (d.b.) was approached.