Composition for maintaining or improving oral immune function

A method for maintaining or improving mucosal immune function, comprising administering a composition comprising young barley grass ground product to a human continuously for 2 weeks or more, in an amount so that the human ingests 0.25 g or more and 10 g or less of the young barley grass ground product per day,

• wherein:
• a content of the young barley grass ground product in the composition is 1 to 100% by mass,
• the composition comprises 1 to 70% by mass of dietary fiber derived from young barley grass in terms of dry mass, and
• the composition is a powdered beverage.