Effects of the amount of sorbed water on the solid-state crystallization of amorphous .alpha.-,.beta.-, and .gamma.-cyclodextrin (CD) were investigated. Water vapor adsorption isotherms were measured at 40.degree.C for each amorphous CD which was prepared by the grinding in tungsten carbide vibrational mill. At higher relative humidities, the amorphous CDs converted to the corresponding crystal CD hydrates. X-Ray powder diffraction measurements were made after the samples reached the water vapor adsorption equilibrium. The crystallization occurred when the amorphous CD took the same water content as that of the hydrate. It was found that .alpha.-CD recrystallized in two crystal forms of form I and form II at 61.5 and 79.0% relative humidities, respectively.