Effects of ?-cyclodextrin, ?CD, on refolding of lysozyme was investigated at pH 12 employing isothermal titration calorimetry (ITC) at 300K in 30mM Tris buffer solution. ?CD was employed as an anti-aggregation agent and the heats obtained for lysozyme+?CD interactions are reported and analyzed in terms of the extended solvation model. It was indicated that there are two sets of identical and non-cooperative sites for ?CD. Enthalpic force in the first binding sites is more important than entropic one, indicating that electrostatic interaction plays an important role in the interaction of lysozyme with ?CD. The interaction in the second binding sites is stronger and both enthalpy and entropy driven but hydrophobic interaction has more important than electrostatic force. These results suggest that the effects of ?CD on lysozyme refolding are attributed to its ability to suppress aggregation of the protein.