Disclosed are: a method for utilizing a kombu (kelp) extract as an antibacterial auxiliary agent； and a method for utilizing a combination of the antibacterial auxiliary agent, lactoperoxidase, glucose oxidase and glucose as an antibacterial composition having a potent antibacterial activity. Specifically disclosed are: an antibacterial auxiliary agent comprising a fraction having a molecular weight of 5000 or less and produced from a kombu extract as an active ingredient； an antibacterial composition comprising the antibacterial auxiliary agent, lactoperoxidase, glucose oxidase and glucose； an antibacterial composition as mentioned above, which additionally comprises xanthane gum； and a food or beverage containing the antibacterial composition.
