The invention relates to an acidic beverage containing aspartame and relatesto an acidic beverage in which a decrease in the sweetness of aspartame mixed withpolymerized polyphenol (particularly polymerized catechin) during storageis suppressed. Further, the invention relates to a method of suppressing a decreasein the sweetness of aspartame during storage in an acidic beverage containingaspartame using polymerized polyphenol (particularly polymerized catechin).