Daily increase in the number of patients suffering from illnesses due to reactive species has induced the permanent discovery and study of antioxidant compounds. The structure, reactivity, and antioxidant activity (AOA) of a phenolic compound named cycloartocarpesin (CAP), evaluated at DFT/B3LYP/6‐31 + G(d,p) level, is reported herein in the gas, pentyl ethanoate, and water phases. Bader topological analysis revealed that two of the three O‐H groups of CAP are involved in hydrogen bonds while the average local ionization energy (ALIE) and appropriate Fukui functions showed that electrons in the near vicinity of C7, C10, and C12 are the least tightly held and can easily be attacked by radicals. Analysis of the transition state of the reaction between CAP and HOO• radical shows that the proton coupled electron transfer process is not favored. Moreover, analyses of electronic spectra calculated at TD‐DFT/B3LYP/6‐31 + G(d,p) has interestingly demonstrate the ability of CAP to filtrate UVA, UVB, and UVC, thus exhibiting a photo‐protective activity.