The effect of (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CyD) on the solubility properties and spectroscopic features of hesperetin and its 7-rhamnoglucoside, hesperidin, was qualitatively and quantitatively investigated in water, by means of UV-vis absorption and fluorescence spectroscopy. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility measurements; in both cases type-A(L) diagrams have been obtained (soluble 1:1 complexes). The higher degree of interaction showed by hesperetin may be attributed to the higher hydrophobicity and smaller size of the aglycone molecule, which therefore exhibits a greater affinity for the CyD and fits better into the cavity. The effect of molecular encapsulation on the two flavanones antioxidant activity was afterwards evaluated by means of different biological assays, concerned to the different mechanisms of in vivo action. The protection efficacy was in all cases higher for the complexed drugs, with respect to the free ones; these results are of great interest for their potential usefulness in pharmaceutics.