It is intended to provide an oral flora-improving agent capable of forming a favorable flora in the oral cavity and a food or a drink for improving the oral flora. An oral flora-improving agent containing as an active ingredient a ganglioside and a food, a drink, or a feed for improving the oral flora containing the ganglioside exhibit an antibacterial effect on harmful bacteria in the oral cavity, which are undesirable from the viewpoint of decay and diseases such as periodontal disease, and a growth-improving effect on useful bacteria to be preserved in the oral cavity. Further, the ganglioside is efficaciously used as an active ingredient in an antibacterial agent or an antibacterial drink, food, or feed, a growth promoter, or a food, a drink, or a feed for promoting growth.