Abstract: The harmful effects of oxidative processes in living organisms, in addition to chemical and biochemical media, can be reduced by antioxidants. The efficacy of an antioxidant depends on its reduction potential and kinetics of elimination of diverse free radicals. Redox potentials and reaction rate constants of selected gallocatechins and flavonoids were measured by pulse radiolysis and laser photolysis. The reduction potentials of the flavonoids studied were in the range of 0.33 V (quercetin) and 0.75 V (kaempferol). The rate constants of the superoxide radical with 15 flavonoids ranged from 105-107 M−1 s−1. Singlet oxygen quenching by flavonoids was also very rapid (from 105 to 108 M−1 s−1). These studies may be crucial in optimizing health and increasing longevity by reducing oxidative stress and biological damage.