Antioxidative activity and protective effect against ethanol-induced gastric mucosal damage of potato protein hydrolysate (potato peptides, Po-P) were studied in vitro and in vivo. The Po-P obtained by proteolysis with Amano P and pancreatin inhibited linoleic acid oxidation either by 83% at its coexistent 0.005% in a ferric thiocyanate assay system or by 32% at its coexistent 0.0002% in a β-carotene decolorization assay system. Meanwhile Po-P were orally administered to male Wistar rats at doses of 12.5-100mg/kg of body weight (BW) 30min prior to ethanol injection. Consequently the ethanol-induced gastric damage was significantly reduced in a dose-dependent manner in the Po-P administered rat. The highest effect was observed in the group dosed with 100mg Po-P/kg BW; the inhibition ratio was 69.6%. The extent of antioxidation or protection against ethanolinduced gastritis was quite similar to those of the respective peptides from casein, corn protein and ovalbumin, suggesting that the potato protein hydrolysate could serve as a useful food ingredient in practical eating habits.