Disclosed are a reduction inhibitory agent for active oxygen eliminating activity, comprising: (a) at least 10% (w/w) of a cyclotetrasaccharide having a basic cyclic structure in Chemical Formula 1, on a dry solid basis; and (b) at least one member selected from the group consisting of saccharides and edible fibers; a method for inhibiting the reduction of active oxygen eliminating activity, comprising a step of incorporating at least one percent (w/w) of a cyclotetrasaccharide having a basic cyclic structure in Chemical Formula 1 to a plant substance, on a dry solid basis, into said plant substance with active oxygen eliminating activity in an aqueous system; and a composition obtainable by incorporating at least one percent (w/w) of a cyclotetrasaccharide having a basic cyclic structure in Chemical Formula 1 to said plant substance, on a dry solid basis, into a plant substance with active oxygen eliminating activity to inhibit the reduction of the activity of said plant substance.