The equilibrium constants for the association of a series of alpha,omega-alkanediols (S) with alpha- and beta-cyclodextrins (CD) in water were estimated spectrophotometrically by the competitive binding effects of the diols on the association of CD with methyl orange. Effects of methanol, ionic strength and temperature on these interactions were also investigated to gain further knowledge on the mechanism of the inclusion process. Moreover, the thermodynamic parameters for association were derived and discussed. The linear correlation between the association constants and the partition coefficient of the diets in a diethyl ether-water system and the constant increment in Gibbs free energy per CH2 group for the transfer of alpha,omega-alkanediols from the aqueous phase to the cyclodextrin cavity suggest that the binding mechanism is of a hydrophobic nature. Furthermore, the size of the cavity of cyclodextrins plays an important role in the association process. The alpha-CD cavity was found to have a greater affinity for the diols than the beta-CD, whereas the reverse is the case for methyl orange.