This paper describes the study of the radical scavenging activity of the natural antioxidants rutin, quercetin, caffeic acid, ferulic acid, and resveratrol by using a substrate-free chromatographic method based on the generation of center dot OH radicals by the photolysis of H2O2 in a photochemical reactor. The comparative studies permitted the classification of some phenolic compounds regarding their in vitro radical scavenging properties (rutin>caffeic acid approximate to quercetin>ferulic acid>resveratrol). The results obtained by the proposed HPLC-UV/H2O2 photolysis method could be well corroborated by the other methods, which employ the generation of free radicals with different reactivity (ROO center dot, , and DPPH center dot). Furthermore, the reverse-phase chromatographic separation of the antioxidants from their sub-products generated after attacking with HO center dot radicals improved advantageously the selectivity of the measured signal used for calculating the radical scavenging activity.