The enthalpy of dilution of dilute aqueous solution of meso-2,3-butanediol, x < 2 x 10(-3), and enthalpy of inclusion of meso-2,3-butanediol into alpha- and beta-cyclodextrin cavities in dilute aqueous solutions have been determined by using a rocking twin-microcalorimeter of a heat-conduction type st 298.15 K under atmospheric pressure. The enthalpies of inclusion of meso-2,3-butanediol into alpha- and beta-cyclodextrins are exothermic and smallest among three isomers, 1,3-, 1,4- and meso-2,3-butanediols. The correlation between behaviors and molecular shapes are discussed.