Oxygen radical injury and lipid peroxidation have been suggested as major causes of atherosclerosis, cancer, liver disease and the aging process. Piperine, having an antiinflammatory effect, has been demonstrated in in vitro experiments to protect against oxidative damage by inhibiting or quenching free radicals and reactive oxygen species and hydroxyl radicals. The effect on lipid peroxidation was also examined and IC50 values were calculated. Piperine was found to act as a hydroxyl radical scavenger at low concentrations, but at higher concentrations, it activated the fenton reaction resulting in increased generation of hydroxyl radicals. Whereas it acts as a powerful superoxide scavenger and IC50 is 1.82 mM, a 52% inhibition of lipid peroxidation was observed at a dose of 1400 microM with an IC50 of 1.23 mM. The results depict that piperine possesses direct antioxidant activity against various free radicals. This study also opens newer views on the potential efficacy of piperine in protecting tissues from peroxidative damage.