Helicobacter pylori(H. pylori)-activated neutrophils produce the oxygen-derived free radicals (OFRs) which play an important role in gastric mucosal cell damage. Rebamipide (2-(4-chlorobenzoylamino)-3-[2-(1H)-quinolinon-4-yl] propionic acid) is an antiulcer compound, which protects gastric mucosa against OFR-mediated injury. In order to investigate the effects of rebamipide on OFR production and to compare the antioxidant activity of rebamipide with those of three known antioxidants, N-acetylcysteine (AC), ascorbic acid (Vit C) and glutathione (GSH), the antioxidant activities were determined by luminol-dependent chemiluminescence (ChL) assay and pyrogallol autoxidation assay. The ChL value was markedly elevated immediately after the addition of H. pylori into the medium containing neutrophils. The antioxidant activity of 1.0 mM rebamipide was greater than that of 0.1 mM rebamipide in the luminol-dependent ChL assay, while in the pyrogallol autoxidation assay, the antioxidant activity of 1.0 mM rebamipide was similar to that of 0.1 mM rebamipide. Rebamipide inhibited OFR generation in the pyrogallol autoxidation assay, with the potency being in the order of GSH > Vit C > rebamipide > AC. In the luminol-dependent ChL assay, the antioxidant activity of rebamipide was the greatest among them. These results indicate that rebamipide is a potent antioxidant and scavenges OFRs produced by H. pylori effectively in luminol-dependent ChL assays.