The standard heat of solvation of beta-cyclodextrin (beta CD) with one mole of water is determined as -10.50 kJ per mol beta CD, after measurement of the heat of dissolution of beta CD samples containing various amounts of water. This value is constant in the composition range beta CD.nH(2)O, with 0 < n < 11 (n is the number of water molecules attached). The thermogravimetric study of the kinetics of water absorption by beta CD does not show a definite hydrate. The water content of the hydrate is controlled by the vapour pressure and temperature alone. Under ambient conditions, the number of water molecules bound to one beta CD molecule lies between 10 and 12.