Oxidative stress is involved in the pathogenesis of numerous chronic human diseases. The objective of this study was to determine whether administration of a decaffeinated green tea extract providing 844 mg flavonoids daily reduced the urinary excretion of 8-epi-prostaglandin F (8-epi-PGF), a product of lipid peroxidation in cellular membranes and of low-density lipoprotein (LDL). Nine healthy male and female subjects were studied at baseline and after 14 days of green tea supplementation. Analysis of urinary 8-epi-PGF was performed using immunoaffinity extraction-gas chromatography-negative ion chemical ionization-mass spectrometry (GC-NICI-MS). Urinary 8-epi-PGF concentrations were 0.286±0.120 nmol (mmol creatinine)−1 at baseline and 0.244±0.177 nmol mmol−1 creatinine after green tea supplementation. There were no significant differences in the excretion of urinary 8-epi-PGF after treatment with green tea. We conclude that 14 days of green tea supplementation did not significantly alter in-vivo lipid peroxidation.