Moisture adsorption isotherms of fuzzy cottonseed, black cottonseed, whole cottonseed kernel, blended cottonseed kernel and its protein isolate were obtained using gravimetric static method at 15, 25, 35 and 45 degrees C. GAB, Halsey and Harkins-Jura equations gave the best fit to experimental data among 14 well-known equations tested. M-0 values of samples calculated by G.A.B. and B.E.T. equations decreased with increasing temperature. The moisture adsorption isotherms obtained were type II sigmoidal. Thermodynamic properties such as differential enthalpy and entropy were determined from moisture adsorption data, using Clausius-Clapeyron equation. The experimental data showed that enthalpy-entropy compensation theory was applicable for the moisture adsorption behaviours of cottonseed samples and the adsorption process of samples was enthalpy-controlled. (c) 2006 Elsevier Ltd. All rights reserved.