Mate (MT) is a popular South American beverage that has been used as a traditional medicine for centuries, spurring recent interest in its nutraceutical properties. MT is prepared as an infusion of leaves from the Yerba Mate (llex paraguriensis) tree. MT has been reported to have antioxidant properties in vitro and in vivo, but these have not been fully characterized in terms of effects against specific radicals. Accordingly, we examined the antioxidant effects of an MT infusion against hydroxyl and superoxide radicals in both chemical and cell culture assays. MT infusions were prepared at 3.10 g/L in boiling water and diluted to experimental dilutions from this stock. Electron spin resonance (ESR) experiments indicated that MT scavenged hydroxyl radicals (produced via the Fenton reaction) and superoxide radicals (produced via the xanthine/xanthine oxidase enzymatic reaction) at all concentrations tested (P < 0.05). Further controls indicated that superoxide radical scavenging was not due to xanthine oxidase inhibition. MT scavenged hydroxyl radicals and decreased cellular oxygen consumption in a dose-dependent manner in Cr(VI)-stimulated RAW 264.7 cells, based on ESR and oxygraph measurements (P < 0.05). Similarly, MT also inhibited hydroxyl-radical-induced lipid peroxidation and DNA damage in a dose-dependent manner in RAW 264.7 cells, based on malondialdehyde and Comet assay data (P < 0.05).