PURPOSE: To improve the anti-oxidizing effect without causing any harm to the human body by using an enzymatically hydrolyzed protein as the active ingredient.

CONSTITUTION: Protein (e.g. gluten meal) is reacted with 0.1-1.0wt.% enzyme (e.g. alkaline protease) at about 50°C for about 24hr to give an anti-oxidizing aid comprising an enzymatically hydrolyzed protein. 0.0001-3.0wt.% antioxidant (e.g. tocopherol) and said anti-oxidizing aid of 1-100 pts.wt./pt.wt. antioxidant are incorporated into an unsaturated oil or fat (e.g. soybean oil), an unsaturated fatty acid (e.g. eicosapentaenoic acid), an unsaturated hydrocarbon (e.g. squalane), an unsaturated surface active agent (e.g. glycerin mono-oleate), or a food or cosmetic containing them.