The in vitro formation of quercetin- and myricetin-cyclodextrin inclusion complexes in acidic medium has been characterized using the enzymatic system horseradish peroxidase, which oxidizes those flavonols in the presence of H2O2. The presence of cyclodextrins (CDs) in the reaction medium inhibited flavonol oxidation due to the complexation of the flavonol in the hydrophobic cavity of CDs. This inhibitory effect depends on the complexation constant Kc between flavonol and the CD type used. The Kc for quercetin and myricetin with the different types of CD used was calculated by nonlinear regression of the inhibition curves obtained in the presence of CDs. In both cases (quercetin and myricetin), the Kc values obtained followed the order hydroxypropyl-beta-CDs > maltosyl-beta-CDs > beta-CDs, reflecting the greater affinity of modified cyclodextrins for the studied flavonols compared with their parental beta-CDs. Moreover, the complexation efficiency (CE) values for HP-beta-CDs and quercetin or myricetin were calculated (267.4 and 5.3, respectively), indicating that HP-beta-CDs are more efficient for the complexation of quercetin than myricetin in the studied conditions, despite of the K c values being very similar in both cases.