The inclusion of acridinedione dyes (ADR) with beta -cyclodextrins (beta -CD) in the presence of 0.6% methanol is studied using absorption and fluorescence techniques. The association constant was determined by using the Benesi-Hildebrand plot and also by nonlinear regression analysis. A stoichiometry of 1:1 was found for beta -CD/ADR (3-5). The nonobservation of the changes in the absorption or the fluorescence in the case of dyes 1 and 2 clearly indicates that the phenyl substituent at the -N atom in the ADR (3-5) is included in the beta -CD cavity. Thermodynamic parameters DeltaH and DeltaS values obtained from the temperature-dependent binding constants of the beta -CD/ADR (3-5) system are reported. In tile presence of P-ca, the fluorescence of ADR (4) dye shows single exponential decay, consistent with the completion of complex formation, and ADR (3, 5) showed a double exponential decay, consistent with the equilibrium between free and complexed forms. The binding constants and thermodynamic factors are systematically resolved through lifetime analysis.