Streptococcus salivarius K12 is a kind of bacteria that settled in the mucosal epithelium of human mouth and nasopharynx shortly after human birth. It is found that Streptococcus salivarius K12 is a probiotic beneficial to human health. Many studies have confirmed that Streptococcus salivarius K12 has bioactive effects against oral and oropharyngeal inflammation and infection, dental caries, halitosis and oral epithelial damage. This paper reviews the research progress of Streptococcus salivarius K12 in the prevention and treatment of oral and oropharyngeal diseases.